Is it fun?
I think so. Fun is subjective.
Good?
The game does have polish. There's 21 characters, and about 6 or 8 maps. The characters are split into four roles, and each of them is easy enough to pick up, but some of them have decent depth. Not a massive amount of content, but I enjoy small bursts of it every day or so.
Balanced?
There's a few issues here and there, but nothing absolutely game breaking. General consensus at the moment is that Widowmaker and McRee are strong, because FPS sniper for the former and a powerful close range stun and burst for the later. D.Va is weak due to a flanking focus with somewhat lacking damage. A lot of new players have trouble with Bastion, as he simply cannot be taken head-on. No character feels helplessly weak, unlike some TF2 classes.
It does help that players are encouraged and often do select decent team compositions.
Gameplay looks like TF2 meets Dota.
I guess. It has a better teamwork focus than tf2 does (at least pub wise), and I think some class roles are executed better than in TF2. The only real dota-like mechanics are the fact that you have abilities on cooldowns, and each character has an ubercharge-like ultimate ability.