It's fun. Playing it during the free open beta on b.net. Feels like a more polished Team Fortress 2 with more character options and more customization. If you like TF2 it is definitely worth giving it a try during the free open beta days (May 5 - 9th).
I haven't played every single character yet but so far every character feels very different and unique! There are four sub-classes (Offense, Defense, Tank and Support). There are 6 offense characters, 6 defense characters, 5 tanks and 4 support so you get a pretty good variety of characters to choose from. Normally I don't like playing healers especially when that is basically all they do but its actually a nice of pace of from time to time to play as healer in this game. They give the healers some pretty cool abilities to make it easier on them and give a slightly different dynamic to the game. For example the easiest healer, Mercy, to play gets a massive speed boost and flies to an ally that is within line of sight. Another healer, Zenyatta, can apply a healing orb to a teammate and as well as a damage boost orb to an enemy.
The sniper, Widowmaker, is actually very viable in CQB and doesn't have to perch somewhere to be effective. At least 1 tank, 1 offense, and 1 defensive have a healing ability so its also viable to play a self-sufficient class, but obviously the game is completely built around team play. Unlike some games that claim to be a team based shooter (looking at you Battlefield 3+) this game completely relies on team play to win and many characters are completely dependent on it. Some of the offense and tank types can go solo for a bit but they will still want to play near their team or come back very soon.
If you're not too much into PvP you can always play against AI with other players. Seems to be a lot of people playing so no problems finding matches in PvP or co-op.
Move over hats there is plenty of customization in Overwatch to make you feel like a special unique snowflake. The characters have skins, opening sequences, voice statements, spray paint (still figuring out what this does), victory poses and probably a couple more things I'm forgetting that all can be customized. When you level up you get a loot crate for free that gives you 4 of the customization options for any of the characters. Pretty sure they will make this a micro transaction for those who have to have appearance items right away, but right now all you have to do is level up to get it.
But ya solid game, definitely worth a try for any TF2 fan and worth a try even if you're not. It's very easy to pick up and be relevant from the start, but there is also so much you can do that it will take time to really learn the game. I recommend learning the characters in co-op (vs AI) as that's the best place. There is also a training ground with dumb bots where you can try stuff out and switch characters on the fly just by going back to the starting room (which you can do in all modes actually) so if you just want to see what's what without any distraction that's a great place.