I've kind of got into this topic late, but here's my 2 cents.
Battlefront 2, in my opinion, looks really fake because of how the AI and human players don't seem to interact with the environment. Their corpses, pickups, bodies when moving, even the bullet collisions (or laser collisions. whatever) don't seem to interact with the world. It's like the motion and actions were recorded in a much simpler, blocky area, and then transfered to the playable area. This could just be bad hitboxes and collision, but it's not quite that.
Here's a picture I found of shadows in BF(1?) and as you can see, they're not even on the ground. They're floating there, inches above the ground.
I've thought about this a long time ago, and it really is a problem for BF1 and 2, compared to games like Half-Life 2 or Call of Duty. In those games, like Rep said a page or two back, you can pick up objects, shoot windows, etc. Basically just interacting with the environment. With CoD (Atleast the MW series) it has a "Press Space to jump" prompt when you near things you can jump over. It's little things like these that make a game seem "real".
Since some people commented on how the Battlefront series weren't really comparable to games like HL2 or CoD, and it was supposed to be cartoony, let's take a game that is in my opinion Battlefront 3, Team Fortress 2. Sure it came out in '07, but it's somewhat of a step down from the graphics of Half-Life 2, but still runs on the same game engine. They (BF2 and TF2) even have similar game modes, so I really think we should compare them.
Here are some samples of what TF2 looked like (It's art style has changed since then. YouTube some videos to see what I mean.) (Also don't look at the videos in the link. They're made with special software and don't represent what the game itself looks like.)
Anyway, TF2 fits with BF2's "cartoony" feel, they have similar gameplay, but the difference is that TF2 looks good or "real" (For a cartoon) and BF2 doesn't. Why is this? Well, I think it's because of the interaction with the environment (Bullet decals, ragdolls colliding with the environment, general player collision, etc.)
I know I wanted to say more, but I think I'm rambling now. You get the general idea though--Interaction with the environment is what makes a game feel real.