1. About the takedown spamming - Shields and Lashley have the highest takedown attempt AI in the game. By far. Maybe not a good idea featuring them in the demo, but that's why the constant takedowns. He also said they will tune it.
2. Ground controls. A lot of people don't know how to posture and sweep properly.
Full guard Top - Down and Y makes you posture up, down and Y again makes you stand over them to rain down blows, A is a small transition(Full Guard to Half Guard) Up+A is Major Transition(Full guard to Side Control)
Full guard Bottom - Press A to go for a sweep X for a sub and Y to stand up, the Rubber guard is in the game but just none of the fighters have it I think.
Remember and look at your fighters special moves.
The ground game is great, remember this is only a demo guys.
Finally, the game is built upon certain realism. For instance, you can't walk up to a wrestler and just brawl Chris Leben style like Undisputed, because he will take you down. Pick your shots, time knees, etc.
Remember, it's a demo with a size restriction from an earlier build. It was just to give fans a taste. If you don't like using the right analog (I do) you can switch to classic controls. Head over to the official EA Sports MMA forums for controller layouts and video tutorials. Do not forget that this game features the best online experience any sports game has ever seen as well as many more fight rules, styles and options. IT'S A DEMO.