general strategy; start games with minotaurs, as their toughness compared to cost is fantastic. ignore goblins and centaurs, they're ineffective. after building up minotaurs, focus on putting the fliers in (vampires and manticores are great). I didn't use Liches and Elementals at all, they just seem ineffective and expensive. in the tougher levels spam Demons (I went with Mage, I recommend it) near the enemy's spawnpoints. use skillpoints to upgrade vampires, manticores, the demon upgrade for sure, and whatever else you like.
strategy for level 4; ignore the treasures in the beginning, because you can't fend off the waves and the guardian monsters at once. build up with Minotaurs, Manticores and maybe a few ranged's (I used upgraded Liches) and keep pushing your hero to defend. put your units in range of the guardian monsters, so when you attack the dungeons in midgame (when your hero is of a decent level) the units can come to your aid.
a good idea terribly executed. to improve it greatly I would make different dice (more than 1-6) and using the total number of dice instead of the "best versus best" roll.
mass of manticores (preferably built by buffers) + traps seems to be everything I need through the entire game. just smashing through level 8 by just starting with minotaurs early and then massive manticore spam.
music in the background, classical, a shop, make it perhaps a chatting game with some additional charm, add more fish and more scenery, etc. also yeah, what the guy said about Facebook. not everyone has or wants facebook.
the ai is decent, sometimes does a sexy sacrifice attack, and seems to recognize some of the openings, but then it horribly blunders at times (especially the king-rook-pawn) endings. also, it's very vulnerable to Scholar's Mate (e4, bishop c4, queen h5, then retreat to f file and continue to attack)
I found it pretty enjoyable, fitting music, easy enjoyable graphics, relaxing concept. the bad sides is how I get autolinked to god knows where when I clicked "new achievement" tab, that you can spend money on upgrade over and over, that it is amazingly short and you get to max everything within a few minutes and seem pretty much OP.