I think Gman hit on a couple of strong points, although I'd like to clarify my own position on them a bit.
When it comes to abusing the ki system in head on charges (waiting around for someone to get close then charging them, stuff like that), I'm not a fan at all. If you don't know what you're doing I can say OK to that, or if you are just inexperienced and it's a method you've found to get in a lot of hits, that's all right. The problem I have is when skilled players use it. If you know what it is, and you know that it gives you an unfair advantage that is unintentional, and you still use it (or worse yet, you get good at exploiting it), it's insulting. I don't play to see who can pull the most dirty tricks. Personally I wouldn't mind if these people would just come out and tell me ahead of time that they weren't going to play fair, but people don't do that.
The other thing I can't stand is killing people in power struggles. I think this "feature" needs to be rethought or removed, personally. What's the point when you're so close to winning and someone just blasts you in the back with a kame? Sure, they could do it to Cell, but he was powerful enough that it didn't matter. When it *does* matter it ruins things (you can't get out of struggles to block a blast).
Bottom line: Tell me if you're going to play dirty pool and I wont mind, but surprise me, particularly if you're an advanced player, and I'll be angry with you.