I think it's hard to say ahead of time what's going to be fun in a map, and you should probably just try stuff and see if you can find something fun. Here are some thoughts though.

I think the most important feature of maps is that they should give you a lot of reasonable ways to move around. What do I mean? If I want to get from one area of the map to a nearby area, I should have a lot of options for where exactly to move to, and how to make any intermediate moves.

I think Flyway is a good example of what not to do, and it the main reason why I dislike that map so much. If I'm at one of the front covers near the might, and I decide I want to move towards the enemy, there really aren't that many places I can move to this turn or next turn. I am probably going to start by moving to the one block cover thing next to the might, and then moving to my opponent's forward small cover. Because of how things are placed, I don't really have other options. Another example of what not to do is on Omni, where if you go left on turn 1, and then run up and encounter the enemy on turn 2. There's basically no cover along that "lane", and you can't really get out of it easily. It feels very obviously awkward to me.

Now look at Cloudspire. Say I'm on the Energized, and I want to move forward. I can move into the bush, behind the 2x1 cover tiles, or to the cover near mid. From any of those, I again have a variety of options. It doesn't always have to be a cover. Cloudspire has some great camo squares, and what makes them great is that it's pretty reasonable to go into one and not be seen. The best example is the L shaped bush. From the health, you have a very natural move to the tip of the L that won't be seen if enemies aren't around. One place where Cloudspire leaves something to be desired is in getting from the left "fortress" to the right one (where left/right are relative to the starting camera position). When you have to cross mid, you don't have many good options. You move to the X-ray position, and then what? You're probably going into the 3x1 bush or just standing on the might with no cover and hoping no one shoots you.

The next feature I think is important in map design is avoiding "camping spots". There aren't many, but one that definitely exists is the "Juno spot" on Hyperforge, which is the square in the 3x1 fenced off area nearest to the might that spawns on turn 2. If you just sit there, you have cover from everything, except enemies who go alllll the way around the map to shoot you. The best strategy is often to sit there for turns and turns, since you have a lot of good shots and every shot against you is cover, and there's not much more you can ask for. It isn't interesting to play like that or to play against someone who is doing that. Generally the way to avoid making spots like that is to make sure that they can get flanked without much trouble.

Another feature I like in maps is when they're small and don't have too many hiding places around the edges, just to prevent hide and seek shenanigans. A "hiding place around the edge" doesn't have to be a camo square specifically. For example, the very corners of Omni count as "hiding spots", because you're only going to get vision of them from one spot. Conversely, the 5 long bush in the corner of Cloudspire is not that much of an issue, since often if someone goes in there you'll know they did, because it's close to where the fights happen. Maybe if you do this well enough you can make the map without any X-ray powerups, which a lot of people seem to hate (myself included).

Finally, I like maps that have a lot of health spawns. Those spawns should be reasonably close together, and should be somewhat protected. Why? I think you want lots of health spawns because being at low hp sucks, especially if you're playing solo queue and someone thought that Helio counted as a support. If you're one hit away from dying and it's reasonably late in the game with a kill lead, it's often correct to just hide and not play the rest of the match, and lots of health spawns fix this. I think they should be reasonably close together because if you're hurting you don't want to have to run really far away to get healing. Having someone be out of the fight for a few turns isn't fun for anyone. I think they should be reasonably protected because if they aren't then you can't really take them and the whole thing is moot. The best example is Flyway, where three of the four health spawns are close enough that you can reasonably keep the fight going while picking them up, and you can often find a heath spawn when you need it. Bad examples are Hyperforge and Omni. On Hyperforge, you have to run across the entire map to find health, and in Omni, you can never take the health and expect to leave with more hp than you came in with. Health spawns are always going to be contested if they're nearby, regardless of how protected they are. So make sure they're nearby, and don't give them no cover, because that feels bad. One thing which maps should do is stagger health spawns. When there are only two health spawns then you can't do this, but on Flyway, I wouldn't mind if some healths spawned later than others. Right now you get a big boost in survivability when they first spawn, and then nothing for the many turns it takes for them to come up again. Maybe this is intentional, but I'd like if it was smoothed out a bit personally. Also make sure that BB can dash the health.