for an open beta moba, this game is polished and boasts extremely fun gameplay dynamics. nonetheless, it is not a LoL/Dota clone, but more of a hack-slash / 3rd person shooter / ARPG hybrid. the hero designs are cool, with skills and graphics that gel really well together. the action is fast, with fantastic rhythm.
gameplay is in teams of 4; and you can arrange with friends in lobby. in PvE there are mission objectives to kill zombies, rescue civilians, defend a supply point, or grab supplies and run. in PvP it's 3 teams free-for-all, where the key to winning is gathering sufficient supplies rather than simple K/D/A or destroying a base. it's a bit of capture-the-flag, defend supply points, be first to kill a super zombie, and stealing enemy supplies (after trucks are filled). suffice to say, the dynamics are very fresh and challenging.
once you start learning your first character, you would be thrilled and thinking, "this sh*t can really go places!" that, incidentally, is what got most of us hooked. of course, not everything is perfect yet, but given time and a steadily-growing playerbase, i am confident that DI:E will make it as one of the better (if not the best) f2p games on steam.
try it out -- i guarantee you will love it.