Competent but unfulfilling.
Avencast is one of the numerous German RPGs running around out there, and the second of which I've played, along with Drakensang. Interestingly, Avencast is hindered by many of the same faults as Drakensang and an inexplicable failure to adapt to modern RPG conventions.
It's hard to speak too harshly about Avencast given the price at which it can be acquired - regularly well under ten dollars on Steam with regular specials. One can certainly get their money's worth if they happen to see no other appealing options, but as an RPG, it's hard to point at exactly where it is that Avencast excels over the competition.
The first place one would have to look is the combat, which is certainly Avencast's most unique feature. Rarely has any game done justice to the complexity of the art of mage fighting. I know that I wonder if I could mumble some complicated incantation while enemies are bearing down on all sides, and Avencast probably makes one of the better efforts at this to date. Players must memorize combinations of key-presses and mouse-clicks to hotkey spells while also aiming and timing them correctly, no easy task, given the relative fragility of the character and the many enemies that are often thrown at him at once. While the player is granted a staff which can do decent damage, he isn't going to ever be wielding a sword and shield that will make his spells anything less than the bread and butter of his survival. There is also a considerable variety to the spells at his disposal, and in playing the game I had at least 5 that I used with some regularity.
However, when viewed as an action game, Avencast suffers due to a failure to make the player feel powerful. It isn't a pretty game to begin with (if I had to guess, I'd say it was built on NWN's Aurora engine, but if that presentation has a particular weakness, it's the fact that spells often feel anemic, with little graphical flare and limited visible impact on enemies. Even after clearing out a room full of enemies, it's hard to feel much like a badass when the destruction you've rained upon your enemies was so underwhelming. So much for being a great mage simulator.
Though the system is still probably more satisfying than an index finger workout game like Diablo, it offers absolutely nothing else that isn't wildly exceeded by that game. (Which is how old now? 13 years?) The story is a cliched joke; the mage academy is under attack and you, a novice mage just come into his own, have to save it. Supporting characters have about as much personality as the Avast! dude who tells me my virus database has been updated, and that's being generous. (Like Diablo, you are a lone adventurer with no party mechanic, you'll only ever speak to questgivers with a few colorless extras designed ostensibly to fill in the world's lore.)
The loot is similarly weak - item drops are fairly rare, 95% of the items you find will be useless, and those that aren't often upgrade you in insignificant ways you truly couldn't care less about.
Avencast is a unique take on the action-RPG genre, and the points where it actually actively offends the player are few, but unique doesn't mean satisfying and I never actually looked forward to my next gaming session with it. Nor did I dread it, it was just sort of something to do, like solitaire or minesweeper. Five bucks is about the right price for that sort of game if you want it, but I can afford to pay more to get more. If you can also, I suggest you do so.