Hours of attractive but soulless tedium.
On paper it looks good. Attractive SF graphics, modular weaponry, magic, hundreds of shapeshifting enemies at a time to mow through...a winning formula indeed. Unfortunately, the execution utterly sabotages any potential it may have had.
The enemies do not actually shapeshift. This is merely the excuse for throwing outlandish enemy models at you. The weapon is modular, but most of the time it doesn't matter, one build will do about as well as the next. The magic is sparse and not terribly effective. When the game actually throws hundreds of enemies at you, the poor controls and camera hurt the fun factor. And it tends to be wave after wave of the same damn enemy, and you have to kill ALL of them. It gets tedious quickly. But not to worry, most of the levels scatter a few small handfuls of enemies here and there, forcing you to hunt for them. A few of the levels I encountered changed up the objectives somewhat, but this mostly made things frustrating.
Also, the game suffers from an epidemic of crate-breaking. This really stopped being fun around the time Diablo came out. These days it's just busywork. Destructible environments (which I hasten to assure you Crimson Sea does not have) are a wonderful thing...but only if it's either tactically useful or an attractive accidental result of combat, not if you have to smash everything in sight for powerups.
By far the worst offense Crimson Sea commits is the story. It's cheesy, it's shallow as all hell, the characters are less than one-dimensional, the voice acting is awful, and you're sidekicked by the most annoying little boy in the history of gaming.
There are other games in the bargain bin for 5 or 10 dollars that are actually worth it. Skip this one.