I have both the PC and Xbox360 version and the game is a lot of fun without mods. Really.
Do Operation Anchorage ASAP. If you play it normally you will get a Power Armor at the end together with training (long before visiting the Citadel) - plus this Power Armor is nearly indestructible. Also plenty of other guns (like a regular Gauss Rifle - the gun is awesome

).
Now, the game is fun in general, with no glitches - they're a lot of fun for a 2nd or 3rd playthrough to fool around. Just don't hurry with the main story line and always look around - there are so many hidden things in the game, small stories for most places you visit, it's really giving the game a Fallout-feel.
As for the addons... I'd say Point Lookout and Broken Steel are the best. Then it's Operation Anchorage (it's more of a shooter - you get health replenish and almost infinite ammo and just plow through the Chinese enemies). The Pitt and Mothership Zeta as the last ones (even though they're fun - just the least fun).
Finally, there's also another glitch with the Operation ANchorage add-on: all the items inside the simulator are indestructible and there's a way for you to "pull them" out to the "real" world. There are walkthroughs on Youtube. Also, when almost at the end, steal a minigun from one of the US soldiers, go back to your camp, drop everything but the minigun and ask for more ammo - you will get some ammo for your minigun (even though you can't get it normally). Now, drop the ammo you got and ask for more... drop the ammo again and ask again - and so on until you're satisfied (I got like 150k rounds when I got bored

). Use the glitch to get an indestructible Minigun and Gauss Rifle with A LOT of ammo for the Minigun (Gauss Rifle ammo is easy to get). Use to glitch and you will have an indestructible Minigun and/or Gauss Rifle plus the "normally" indestructible Power Armor

Now the fun begins
Edit - as for the looks, sure, the PC version looks better but the game is so much fun you don't notice it, really. I can't even tell you what looked better on the PC (I had a HD4870 when I ran it - at 1920x1080 with AAx2). I guess the world/textures were a bit sharper and the framerate a bit better. But nothing to really shout about. Now usually I laugh at people who say the consoles can offer a similar level of graphics to a modern PC but this game isn't new in the first place and it wasn't beyond incredibly looking to begin with. The PC looks better but it's still fun on the Xbox. Can't tell you about the PS3 version - though I remember reading it did look worse than on the Xbox (and that's why it may be more noticeable).