I wouldn't up the ante because they need the money to make the action scenes clearer, and the TFs need better character development.

 

Longer car chases/fights. Bonecrusher vs. Prime was a little short. Triplechangers I think would be the smarter move to go with over combiners. Of course ILM will have it's advances and the robots will look even better. I'm not how a sequel can do any better. The movie was great

 

I'd hope for a greater use of vehicle modes during battles.In the movie, Only the decepticons seemed to be using their vehicle modes well in battle, but it's mostly just confined to hit and fade tatics. Even though we already had impressive sequences such as Starscream vs the F22s in this movie, I really want to see the Autobots make use of their car modes more in battle. I'm reminded of the scene in the G1 opening credits where Skywarp grabs Jazz and throws him, but Jazz transforms into vehcile mode, spins around and transforms to robot mode before leaping back at Skywarp. Or when Prime used his truck mode to crash into Decepticons in TFTM 86. I think if in the next movie they are able to choreagraph fights that successfully intergrate and fully utilise Transformer vehicle modes, it will definitely make the battles a whole lot more interesting.

EDIT Think Hot Rod vs. Galvatron in TFTM '86

 

Let's see. Any one of these would work.

Megatron Comes back, maybe as Galvatron.
Him and Starscream have to have some tension.

Dinobots! Or at least Grimlock. Swoop being my favorite but, Grimlock is always the show stealer.

Prowl, Hot Rod, Sunstreaker, Mirage, Wheeljack, and Springer.

Skywarp and Thundercracker

The Combaticons.

Reflector, one of the coolest toy's and slickest looking animated characters, so underused. A lot could be done with them.

Huge battle on Cybertron. Nemesis vs. Ark battle.

Soundwave period!

Just no Unicron, FF2 already pulled that garbage!

 

Devastator. Versus. The. Dinobots.

Now that would be a kicking fight scene.

 

Sequel needs....

-Combiners
-Definately a return to Cybertron
-This may sound weird, but I would love to see a few more Beast Wars characters thrown in. Maybe BW version of Thunderbolt?
-Some new environments... rainforest or jungle comes to mind.
-Baseformers
-Unicron
-Somehow bring back Megatron. Possibly as Galvatron

 

Ultimately, really only two things now that like, the absolute minimum of Audience Disbelief Suspension (tm) has been reached, and you can push it forward a couple notches.

1) More Space Adventure!

2) Giant Robots making Bigger Giant Robots. Not like having babies, though. Like Cheerleader Pyramids, but with more giant robot faces and smashing.

Of course they're going to add a number of new characters and whatnot, but like, those are the two crazy things like, old ladies would still have their old blue hairs blown out by.

 

A fair bit of what has already been said...and I dunno, Nemesis Prime would be cool to see.

 

Take a leaf out of Star Wars Episode Three: One huge epic battle montage for at least 10 minutes, perhaps in Cybertrons past.

More characters either side, up it from five or so a side to fifteen at least.

Aerialbots vs Seekers

Do not have Megatron jump out of the sea yelling 'I'm Galvatron now!' - way too quick for that.

 

The Dinobots and Constucticons would be cool but I want to see more interaction from both sets of TFs - Autobots and Decepticons and less of the shaky camera effect please!  

 

NO UNICRON

And a good transforming car chase would be nice. The only thing really missing from this film.