During all these fights you're always supported by 2 Bots which help you against shielded enemies or simply can be used to get rid of smaller enemies. They are also used to deploy explosives (when you have to blow up something really big) or hack some terminal to open doors etc.
Another big difference RC veterans will notice right away, is the control scheme. The default setting is now on the sideway style you could enable in the configuration of the previous titles or got when holding down ... I think it was L2. That said, the controls are as great as always, so there's nothing to complain about on this side.
Also the graphics are great and the levels all look different enough to be at least partially memorable.
The game also has (at least for me) some problems, though. First of all there is less to explore. Yeah, no real levels, so no place to hide stuff, I guess. All you can do is collect some achievements (like when you should only with the sniper rifle etc.) and level up your guns. And here we come to the 2nd problem. I basically completed the whole game with only 3 weapons: The rocket launcher, the sub-machine guns and the sniper rifle. The others are more or less ... optional. At least they were for me. I actually never used the shield gun, nor the turret thrower. This balance was IMO in the previous games way better.
The last problem I have with the game is its humor. While RC1,2 and 3 were throughout funny for me, Gladiator feels different. Actually only the audio comments during the game were really entertaining (the male moderator (coward) makes jokes and the female simply wants to see you die). The videos were completely the opposite: IMO nothing funny in there. It was also strange because the videos seem to have been inserted sometimes at simply random occasions. For example: Once I switched the PS2 off right after finishing one out of 3 challenges. And when I started the device again, I was suddenly greated by a video sequence. Strange.
Anyway: I still liked the game. It was not as great as the first 3 parts of the Ratchet & Clank series, but still good.
P.S.: I can't really say anything about the multiplayer aspects since I only enjoyed them for an hour or so. And "enjoyed" describes it quite well :)
Sorry, was too lazy to also write a verdict :-)