5. Massive Body Count
Remember the scene from Return of Jedi where an imperial officer was saying? "We need more men..." Well as an IG player there the issue of having not enough men should be the least of your concern. Swarming your opponent with hordes of men with guns is a very possible scenario.
4. Inferior Complex with a Point to Prove
The fluff has it we petty humans are always being pushed around by the ravaging alien hordes that roam around in the 40k universe. Well by play IG the player can put the theory to the test and guess what? As an IG player you practically has nothing to lose (Hey, we are only humans) and everything to gain (My men best an alien/astrates strike force! Yeah! Take that you **** !).
3. Big Guns, lotsa them
One thing the current guard codex can really do is to rain down on your enemies with big big guns, and you can get a ridiculous them with the current squadron rule. Taking the advantage of the new rule one can run the dreaded "Eat Dust doctrine" (named after the notorious artillery spamming play style in Relic's Company of Heroes where dust fly all over the place when the firing commence) and ground your enemy to dust.
2. Big Tanks, lotsa Them
Ask a guard players the reason they play the army chances are 4 out of 5 times the player in question is a fan of heavy tanks, really really heavy tanks, and the current guard army can really field a lot of really really heavy tanks. So the Leman Russ obsession continues.
1. Hammer of the Emperor
Seriously, with the most numbers of war machines in terms of both variety and numbers and legion of fighting men at their disposal the current guard army can literally smash your opponent flat if done right (i.e. leaf blower army), and as a decent gamer who wouldn't enjoy the scene of your army marching over your opponent's fallen bodies in legion?