With the current offering, I'd say the single-player is good for one to two thirty minute matches once the novelty of playing a brand new game wears off.
The Tournament mode is utterly simplistic. Basically you get a text ordering of Ranks 1-8, display of Ascension Points and the number of matches left. You click a button called "FIGHT!" and it loads the next map. No story telling, no creativity, no eye candy, nothing. I can't even play Demigod Barbie Dress Up with my Demigods by earning new adornments and trophies. It works, but wow, utterly stale match setup and progression flavoring.
The core gameplay is fun with decent AI (it'll kill you if you're lazy or foolish) and with 8 demigods with different powers and strengths there is a lot of replayability overall. But it really depends on if you feel like playing a Demigod who's style you don't enjoy much.
So yeah, good for a quick 15-30 minute fix. It's not something that will keep you glued to the monitor for hours on end throughout the day as a singleplayer game, like an enthralling RPG or TBS/RTS would.
('-')y