This is probably the best and simplest answer to give.
I played Live 15 today and while it has it's share of issues I can see why people like the game. Typically the biggest knock on 2K is the "canimations" which are more or less absent in Live. Now my issue with Live is that after that initial feeling of responsiveness there are a lot or negatives to find.
I think Live has a great foundation to built on. if they can maintain the feeling of control, improve the overall quality of animations (which can be quite ugly), and just improve the overall basketball intelligence of the game and AI then they can be a real competitor to 2k instead of just being a second option.
Can't wait to see how much Live has improved this year when the demo drops next week. The Live team always talks a good game but the execution doesn't always live up to the hype. We'll see if this is the year they can finally deliver on their high expectations.