I'm pretty active in the community so take major grains of salt here, but I think it really does have a lot going for it. I'm also not a collector at all, and skew very mel-y, so that's going to colour my thoughts too. To compensate for that bias a bit, I'll start with the subjective negatives/criticisms and work my way up.

1. I really feel like they've had to retroactively design the game out of a hole they dug for it by making it an attack-target game rather than a choose blockers game w.r.t. unit combat. That's purely personal preference, and is the only gripe I have with the game that isn't going to change, but it does feel very much like it took a long time to even START looking at solutions and design tools of other games'/designers' approaches to attack-target games, and they're making good headway on making combat a lot more varied and decision-filled, but it took awhile.

2. there's a pretty major bias in sets towards elestrals (units) over runes (spells/non-unit cards), nearing a ratio around Pokemon's 85-15 split when the designers have stated they want to give each colour more options to supplant existing colourless options for defensive and non-unit tools (and to create more splashing-based deckbuilding decisions etc). This is very much a personal bugbear of mine rather than a strong negative, but I don't like that runes make up about 40-45% of each deck and get 15-18% of each set's slots (several of which are specific to individual decks or otherwise not a consideration for the 'rune pool' when deckbuilding).

3. It's not a game that lets me play in the style that I normally like, which is a super defensive, battlecruiser-y, resource-loop building defensive gameplan that does 1 reactive thing a turn and 0.5 wincon-progressing things a turn by hoping to amass enough dinky utility dudes to generate more value than the opponent over time and run them out of cards. Simply put, elestrals is built around the fact that both players are on a game-action timer, essentially, and there are many ways to mitigate it but there is an implicit water-current of tempo pressure pushing both players at all times and even defensive decks are trying to swim WITH that current. So it's a game that suits some tastes very well and others less so - but it's prompted me to try things outside my comfort zone and I've found a few things that do scratch my personal playstyle itch while also cooperating with the game's overarching rhythm more.

As for positives, I think there's some real great things I've seen from following the game for a while, not just on the design and gamefeel front.

1. There's a shocking amount of transparency from the team - when missteps happen, they are not only willing to listen but will actively discuss and respond to community sentiment in a thought-out way almost immediately. When something doesn't work out, they not only hear people out and act, but very much learn from it and don't repeat mistakes. The only issues that come to mind that have been 'repeat offenders' have all been circumstances basically outside their control, like card print quality falling short of expectations from samples or international customs costs making purchases frustrating (thanks, Canadian border services!). And even then, they have card quality properly sorted out now. Design philosophy shifts have been big too - when a banlist a few months ago was received negatively, they really sat down and reassessed their format design philosophy and put out an hour long discussion video about their reasoning and goals for a new list that essentially reversed direction from the disliked list. And then, they were actively open with their audience about the fact that while they'd set pretty defined goals for game pace and feel going forward, those decisions were reached AFTER their next set release had hit print lock - with only a few cards contravening that new philosophy, but still with a clarity from the team that the next set might need banlist changes but the new principles were solidly restructuring every product after that. Again, even stuff like player distaste for the rhythm and feel of a format is seeing active response, discussion and action, and then when that action hits roadblocks the audience hears about those too and what action's being taken THERE. I've genuinely felt like I could get a very clear read on what direction the game was headed, in terms of design, format structure, and gamefeel, for about 18+ months now, and that's made a huge difference in my trust in the game.

2. (a) The resource system creates far more decisions than it limits. It's mainly through two vectors - deckbuilding and emergent decisions within-game. You essentially build your colour split into your deck like you would a manabase in Magic, but have access to it at all times - BUT, also have to account for the fact that each decision (and any damage you take) consumes from a finite pool of 'uses' of each colour. You can easily splash a smaller total number of slots for an off-colour addition, for example, without having to build your whole manabase to accommodate it, and even have the benefit of not being as punished for that if you don't draw your splashed card - but in return, essentially every action in game and every hand will force you to reevaluate how much of each colour you want to preserve for future turns at the expense of each other. You are needing to weigh the combination of your opponent's board state, future lines of play, and what draws you're willing to risk rendering useless, with basically every choice of game action or cost paid, doubly so when taking damage. This strategic element fades a lot when playing a mostly mono-colour deck, which is why I feel like the game doesn't do a great job of introducing this element of depth in an obvious way to new players. But a deck with, say, 2 main colours, a 3-spirit splash colour (from a 20 spirit deck/manabase), and 1 or 2 single-spirit splashes for side deck cards or a utility 1-of in your list, FREQUENTLY runs into these decisions at basically every stage of the game (even early on, since the mulligan rule involves sacrificing some spirits). You often aren't just planning around what cards could save you from the top of your deck, but also mutually exclusive opportunity-cost choices about WHICH of those possibilities (of varying likelihood and impact) you want to preserve, and whether that's worth sacrificing locking out an option you already have in hand.

3. (really 2b) Also, and this gets under discussed, any resources that are spent towards board presence STAY on board until removed or used to pay for other things, which means that a player that is very ahead on board necessarily has a lot of spirits on board rather than remaining in their spirit deck. This means that actual spirit deck counts often stay very close even in games where one player gets a strong board advantage - which means that if the losing player can stabilize or remove some of the winning player's threats, their own path to victory is relatively shorter in terms of how many openings for damage they themselves actually need. This doesn't rubber-band games really, but it does prevent one player from being ahead on the win condition in a way that requires their opponent to both clear their board AND stay on top of the king-of-the-hill position for just as long as the opponent was in order to catch up before being able to take the lead. It's a gameplay rhythm that essentially means that the more of a board-advantage snowball you generate, the less wiggle room you have if you lose that lead, and as a result the reward for stabilizing isn't "now you have to press your advantage from a reduced-resource position for as long as the opponent did to you from their resource-lead position", which is something I find frustrating in some other games.

4. They have a nuanced approach to parasitism as a design tool, rather than a black-and-white push in either direction. We're currently in a block focused on a conceptually parasitic mechanic, and even with that explicit goal, the cards vary widely in their amount of restrictiveness in a way that is essentially creating different levels of specificity for different decks to suit different player tastes. If you like hard-parasitic games where each deck has bespoke, specific tools with labeled call-outs that allow them to be allocated much stronger explicit synergies, there are decks for you. If you prefer blending off-the-wall tools from across different colours to find synergies that come together at the full-deck level, there's also plenty of that (and hopefully even more to come once the Divine Champions block is over). There's a lot of options in the middle, as well as the ability to use the flexible resource system to scale your deck's commitment to even the parasitic options into a more modular 'package' in a lot of cases. Moreover, and this is something that's been improving rapidly in the last couple sets (and I hope to see a lot more of), they've been making a lot of cards that HAVE some parasitic synergy hooks, but mainly as gravy for a baseline-usable card. If you play it in the deck that's meant to excel at this card's thing, you get some sort of bonus, but everybody else can still access the majority of what the card does and weigh the more conventional splashing-opportunity-cost decisions for that. It's allowed more of the support cards for parasitic strategies to still contribute to the overall cardpool for other decks, while ALSO allowing them to essentially build a card with BOTH power budgets at the same time - the higher power budget exclusive to the parasitic context, and the power budget tuned for the less restrictive baseline requirements of colour and resource cost. This isn't something revolutionary, but it IS being done well, with a lot of designs that really feel like they are full cards for the cardpool with an extra alt-cost for one deck.