DMC4 has it's own problems, one major of which being it's basically the same half of the game twice just as a different character. The levels are a near identical re-run which makes it feel cheap. If you like the style of Bayonetta and enjoy the gameplay, go for it, if you don't mind the style and gameplay is first, go for it. It does play alot like DMC once you get over the different visual approaches but I suspect you get a better overall package with Bayonetta. If you have a PS3 capable of running PS2 games however, I suggest trying DMC3 which I prefered to 4 despite the shiney visuals or if you really want God of War, why not get the God of War Collection?
Bayonetta is by no means bad, it was enjoyable as a game, play in quick bursts and leave it, but is it's gameplay massively better then something like Devil May Cry? I don't really think so, but some people do like Bayonetta despite disliking DMC (maybe it's the hot chick?). The thing I find with these high paced major over the top hack and slash type games is that I don't want to pay full price due to the length which is why I seek older and cheaper versions because they are all often very similar. Dodge/block then counter and attack. Someone who's more into them may be able to offer better advice but as I said, it's not bad and if you really liked the demo go for it, try the DMC4 demo as well for the hell of it and see what kind of prices you can find for both.