I don't want any combined Transformers unless they're done well. They seem too tacky if they're all transforming and fitting together in the air.
For the sequel, I want Starscream returning with his own Decepticon army (with Soundwave!) and begin attacking oil and energy facilities in order to gain Energon. The Autobots respond, and the two groups fight again. Because the Decepticons are all charged up, maybe they win. Either way, Megatron returns from the depths of the ocean, powered by the Allspark with a new transformation...
And if they do a third movie, they have to do Unicron somehow.