The game itself is fantastic! If you have a group of friends that want to all get together and play it, all the better.
BUT. If you plan on playing alone in the open lobbies, heed my warning... the ingame community is second only to Dota/LoL when it comes to scuminess and♥♥♥♥♥♥♥♥baggery.
They'll kick you at the last wave of maps and invite their buddies to feast on all your hard work building/upgrading/repairing. This is epcially infuriating on maps which have 35 waves and can take HOURS to complete. They'll call you every name in the book, but only because mommy cant see what theyre saying to people online. They'll scoop up every piece of gear they can in between waves, and kick you if you attempt to get to any of those pieces before they do.
In all... don't rely on the online in game community to enhance your experience, instead focus on leveling one of each hero and doing everything by yourself or with friends.