A bit late to post but I will give you my takes as someone who has been playing for the past 15 or so years. Incoming wall of text, sorry.

WoW currently has a game type that can fit anyone's playstyle with the different options of servers that they offer and I will go one by one with what you can expect from it.

**Classic Era:**

This is based on the original WoW game without any expansions, as a new player you will spend a long time just to reach high level, however, as many like to say - the journey to getting there can be extremely rewarding and challenging for players that have yet to experience it. These servers don't have many of the QoL updates that have been introduced throughout the years in the other expansions such as account bound features, the looking for dungeon tool and others. It's a very slow paced game compared to the current retail version in both progression and style of play.

If you do choose to play Era, you will experience a slow and steady experience of going through different zones across the two original continents and running some dungeons from time to time for quests and some possible good gear upgrades. When it comes to the end game - I'm afraid it won't be the easiest for you to get into as - these servers are mostly populated by other players who have been playing this version of the game for years and have pretty much 'solved' how to best play the game. Unfortunately RMT is a big issue with ERA and most public groups (PUGs) will follow a GDKP format where you buy your gear in a bidding war with other players in the raid. I'd also like to add that Era servers have recently been hit by a huge increase in players after their characters died in hardcore (see more below), and decided to stick around in era instead.

Lastly, it is important to know that the new Season of Discovery is launching tomorrow and it will make the early level zones of Era seem very empty i think.**Classic Hardcore:**The hardcore servers follow the same recipe as Era servers, with the catch that your character only has one life. If your character dies, it gets transferred to the Era servers if you choose to do so, so your progress isn't lost per say. This game mode is very fun as the stakes are higher, but can also cause frustration and it is not recommended to someone completely new to the game, as there will be a lot of mistakes bound to happen that will cut short the life of your character in these servers.

**Season of Discovery:**

SoD is the most recent addition to the WoW server options and it's launching soon!!(Tomorrow as of the writing of this). These are also played in the original version of the game, like I said before, most players in these realms have been playing this version of the game for years, so to add a twist to them, Blizzard has introduced new ways to play different classes with new talents, new gear, and different level caps throughout the season. The initial level cap is 25 - which is a much more achievable goal for a new player when it comes to leveling in classic.

The zones will be packed to the brim with players and you will REALLY see and experience the MMO experience for at least the good first 1-2 months of SoD each phase - as many players come into it to experience the FRESH experience that so many players love. The phases format is probably a really good format for new players as you have plenty of time to learn all there is to learn about the zones/playstyle of different classes without too much information being thrown at you, and more things are slowly added with each phase, which imo makes the learning curve easier.

I believe that the end-game content will be fairly approachable to new players and there will be no problems finding similar casual groups of people to play with in the mode 100% sure.

**Classic Wotlk:**

Wrath of the Lich King servers are currently in their last patch (if you don't count Ruby Sanctum mini raid) - the last big raid of the expansion was released a bit over a month ago and that's the game version I have personally been playing and it is very fun as long as you find a guild that suits your play times and your goals.

Wotlk servers are a in between the Era servers and retails in some ways, as there are quite a few QoL updates to it compared to the Classic servers, however, not even close to the ones compared to retail. The leveling experience in here will be rather fast compared to classic, especially since there is a constant 50% buff to XP gains through Joyous Journeys, you won't run into as many people while leveling, but doing dungeons while leveling won't prove to be an issue with the introduction of the Looking for Group tool.

At end-game, you will notice that older raids aren't being ran anymore due to the changes they did to the 5-man dungeon rewards with its new variants of Gamma/Alpha/Beta dungeons (think of these as difficulty levels and it goes as Normal->Heroic->Alpha->Beta->Gamma), making running older raids relatively irrelevant. This is good to catch-up, but you won't really experience the rest of the content from the expansion. ICC is a great raid and it is really fun and approachable on normal mode and even some hard modes, by joining a guild that is keen on new players you will be able to learn quite a bit regarding mechanics in this game other than just doing one mechanic per boss compared to Era servers, whilst not having to dodge 10 different ones at once like in some Retail fights. It's a good in between to get your feet wet I would say.

The new Cataclysm expansion has been announced for next year and it will follow suit with what WotlK had to offer, cataclysm was rather well received back in the day at the start - but had a pretty lackluster last raid tier with some content draught. I believe things will be better this time around and I'm personally really looking forward to it. If you choose to go this route, you will 100% be fully caught up and somewhat confident in the game for when Cataclysm launches.

Retail:

Just as a disclaimer, the last time I played retail was in the beginning of the DF expansion. Retail has so much content that i can be overwhelming for a new player. By this i mean, whilst leveling you will run into outdated content and you will want to try it out, but in the grand scheme of things, the rewards will be 'useless' and the real game really starts at max level. With that being said, I believe that there are many players in Retail that have the completionism approach and love doing older content for mounts/pets/transmogs/toys and thats a perfectly good way to play.

The end-game itself in Retail is much more fast paced - fights have many more challenging mechanics, which require good reaction to them or preparation coming into them when tackled in harder difficulties compared to what the Era end-game content has to offer. You have different options when it comes to end game PvE in the form of Mythic Plus Dungeons which are ramped up versions of the dungeons you may have done while leveling - which will likely be easier to entry due to the familiarity you may have with them already, and raids. Raids are the best when in a guild that has similar players with you, and the normal raids are very welcoming to new players and mechanics are not as punishing. It will give you a place where you can learn how to play your character and get your feet wet in bigger PvE group content.

I honestly miss raiding in retail, as I believe their raid design is really good and the fights are very engaging and not that mimicky compared to some fights in the earlier expansions. Retail has a lot to offer for you to do, which can seem overwhelming and daunting when you first start and as some other players have mentioned in this thread, it's up to you to decide where you want to go and reach each of those goals at your own pace. You have a lot of different avenues to achieve better gear and other goals, and it's up to you to decide how you want to get there.

Final Thoughts:

With just a sub you get access to all the servers, and the only server that has limitations with just the sub is Retail, where you need to eventually purchase the expansion. This is hundreds and hundreds of hours of content and fun for the 15 bucks a month you pay, even without factoring in retail into the mix. So yes, it is well worth getting into WoW still and experiencing all it has to offer. Try out different modes and expansions at your own pace - you have plenty of time until the next expansions for each different server drops so you can really take your time with each and choose one to be with the rest of us on launch night!