M.Bison might not have any changes on the surface but the addition of EX moves changes him a great deal.
He's equally comfortable at being both a defensive and rushdown character, and can switch between the two styles during a match.
The key to mastering M.Bison is learning his combos and learning how to manage your meter effectively, as you'll be relying on EX moves a lot to deal damage or escape pressure situations...
Psycho Crusher (back, towards + P)
Don't randomly throw this move out there. That's the classic sign of a noob and it will get you killed, because the recovery when blocked is enough for your opponent to land a free combo of his choice. The EX version, however, is good for escaping corners as you will pass right through your opponent. This move breaks through Focus Attack.
Double Knee Press (back, towards + K)
Also known as Bison's scissors kick. This should be your natural combo ender of choice and, when ranged properly, is safe on block too. This is Bison's main tool for harrassing opponents and frustrating them into making a mistake. The EX version goes through fireballs.
Head Press / Skull Diver (down, up + K then P)
This is a key move for Bison. The standard version is good for punishing reckless projectile throwers but, more importantly, the EX version allows Bison to get off the ground safely and immediately counteract if the opponent was pressuring him. For example, if Zangief tried to Spinning Piledriver M.Bison as Bison was getting off the ground, the Head Press will lift Bison away safely and bring him crashing back down on Zangief's head. The punch follow up is also useful and can be linked into further attacks.
Devil Reverse (down, up + P then P)
This move allows M.Bison to build up his meter from a full screen away, which is good because not only does it mean you'll be building meter for EX moves but it also means your opponent will feel inclined to get close and stop you. Bison can struggle to get close to his opponent, so forcing them to move and take risks can help unlock their defence.
Bison Warp (towards, down, down/towards + PPP or KKK)
Bison's teleport isn't quite as quick as Akuma's or flexible as Dhalsim's but it can still serve him well if there's no EX meter to burn through. Try cancelling a blocked or connecting normal move into the Warp to increase the chance that you teleport away without getting hit.
Knee Press Nightmare (back, towards, back, towards + K)
It's unlikely you'll ever have enough meter for this Super. Rather, you shouldn't ever have enough meter for this Super. Instead...
Nightmare Booster (back, towards, back, towards + KKK)
This is M.Bison's big damage dealer. Comboing into it can be hard, with the two most common ways being from an air-to-air MP or after a Focus Attack. You can also use it to go through fireballs. The threat of it will make players respect M.Bison on his wake-up too, as the Ultra will blow through any attacks to connect on Bison's opponent. If it's blocked, however, you'll be in trouble.
Basic Combo: Air-to-air MP > MP > Nightmare Booster
Advanced Combo: Cross-up HK > cr.LP > cr.LP > st.LK xx Double Knee Press