In a recent interview with Autodesk (developers of Maya), Sam Sharit talks about Insomniac's proprietary game engine, the technology that went into Resistance 2 and other very interesting topics.
"For Resistance 2 we hovered around 5 to 10 thousand triangles. We actually count in quads at insomniac so that would be 2500 to 5000 quads. This is an average, but for things like bosses we go as high as 60,000 tris. However, as I said, it depends on the game, so a game like GTA is going to have lower counts due to the sheer number of assets in the game."
"Insomniac uses its own in house engine. The PlayStation 3 engine was developed for Resistance: Fall of Man, then iterated on for Ratchet and Clank Future: Tools of Destruction, and even further iterated on for Resistance 2. Insomniac has been my first experience working with an in-house engine and I really like the level of control of working with one. One major reason is that it is made to take full advantage of the PS3 hardware, and I have been able to really push some key assets, like the 300-foot tall Leviathan, much further than I would have been able to using some of the other commercial engines on the market. It also allows the artists to dictate to the tech and tools programmers what tools and interfaces we want, and how we want to use them. I find with most commercially available engines the tools are dictated by the company creating the engine, and this may or may not be good for what type of game you're making or your company's established pipeline."