So, right now, my game is heading towards the (first) Battle of Geonosis. I wanted to do it justice, so is there any way I could make it interesting? I'd like to avoid doing mass combat, since no one in the party seems like they would lead more than 6-7 Clone Troopers. from AToC, it seemed like the battle was relatively undefined and it mostly focused on what Obi-Wan and Anakin were doing while the battle was going on.

Not all of the Jedi in the Battle of Geonosis lead Clone troopers. So, if you want to keep the main battle in the background, go for it.

I never ran the First Battle of Geonosis, but instead one for the Second Battle of Geonosis. Rather than focusing on the slaughterfest of the main ground force (like we see in AotC) I suggest doing a sort of Republic Commando-style mission, where the big battle is happening in the background, but your party is focused on a specific objective that has an influence on the battle. Mine was a munitions factory in a cliff that supplied the Hailfire droids their missiles and refill drones. You don't have to have a PC be a leader for your mass combat rolls, but instead a Clone Commander NPC to fill the role if need be. I had a player that had his first attempt at leadership, and had 6 AT-TEs at his disposal, along with a platoon of clones. He got creative and was a great success at the assault, despite being outnumbered and (initially) outgunned.

Okay, what are the major impressions from this battle? A battlefield littered with robots and clones, no real sense of loss except for the expense of it all (clones and droids just being manufactured fodder), smoke & debris, the smell of cinders, fleeing Geonosians, fleeing CIS forces, etc...

Maybe you can't be IN the battlefield, but you can impress upon them what it is like. Maybe their part is simply pursuing some bad guys through a hive factory and do that whole factory cgi episode? They'll certainly need a little part to do. Or, they can command some mass combat vehicles or artillery as Gameboy said. You'd have to get a pretty good grasp of vehicle weapons, stats, and combat to do that, though. Alternatively, they can be a cleanup crew who comes in just after the battle. Maybe they are scouts just B4 the battle? Lots of possibilities.

I would suggest not rolling for Mass Combat and just using that as the backdrop for the battle, unless you are rolling Mass Combat for the small part of the battle the PCs are participating in. For something like commanding artillery or something, it may be best to handle it narratively rather than actually rolling for it. "Hold the droids off for 3 more rounds while the artillery recharges, then they will clear out the approaching armored column." that sort of thing.

Proposal of mine from another thread:

New idea for PCs participating in a large battle:

Each round, make either a mass combat roll or another relevant skill roll (eg, Stealth if the PCs are trying to keep a low profile). Success or failure determines narrative facts about how the battle is going, whether the PCs' mission is succeeding, etc. Despairs or Threats rolled result in enemy forces (minion groups or squads) "breaking away from the main body of enemy forces" to engage the PCs' force. So the rolls determining the outcome of the big battle also help determine how difficult of a small-scale fight the PCs have to face.

Example: Round 1, the PCs are closing in on an enemy base in their fighters, with a single minion group of TIEs pursuing them. They roll a Mass Combat check, or a Knowledge: Warfare check from the PC squadron leader, or something similar. The result is success with Triumph and 2 Threat. For the success, the PCs close in on the enemy base. For the Triumph, the force field protecting the base's hangar goes inoperative. For the Threat, two more minion groups of TIEs break away from the big battle to start fighting the PCs in Round 2.

Back in the Saga days we started a campaign with the battle of Geonosis. I ran it basically as the first mission from the Republic Commando video game: the PCs had to locate Sun Fac and bring him to justice. This was tertiary to the main battle obviously, but I still had environmental hazard things happen as they crossed the battlefield that put them at risk.

Also, in general, I typically do what DaverWattra suggested.