On my 9th Bloodline (i.e. playthrough)
Fair to say I'm finding it pretty engaging.
Those that play it through one bloodline, get beaten by the God King and then declare it done are rather missing the point of the game.
As complete each bloodline, levelling up your character and your items, the game responds by becoming harder. The bad guys get fancier moves, better weapons and armour and they get much faster.
There's not much wrong with the gameplay IMHO. Yes it is basically just a little series of one-on-one battles leading up to a big boss a la Streetfighter/Soulcalibur, with added RPG-alike elements for levelling equipment and stats.
But that mechanic is only really a disappointment to those folk that played the Epic Citadel tech demo (and subsequently didn't read any reviews) who decided that was what this game was going to be a multi-player open-ended MMORPG sandbox.
The combat gameplay works very well: parrying, dodging and blocking all take a bit of skill to master and timing can be critical, especially against the higher level enemies. The experience system means there is some room for being tactical with your equipment choices (i.e. fighting with the worst sword to maximise your experience).
All in all, for £3, on a phone, it's a pretty impressive achievement.
Further expansion is on the way too, they've just released an update with more weapons, new bad guy and a Santa party helm :)