[neferhet]

I've played a little bit of guard with mixed results. Usually you might want to have 2-3 blobs with commissar/priest and some meltabombs and poweraxe. The guards are fine with grenade launchers.
Those guys need to be supported by some tanks: i suggest wyverns, executioners and maybe some eradicator if your meta has lot of cover. as antitank i suggest you grab a couple of the "start collecting" Scions boxes and use the formation therein. a couple of deepstriking , recycling squads of scions with meltaguns, two tauroxes with scions command squads as support for the blobs...sounds fun. if you have enough points you could also take a couple valkyries or vendettas with some flamer teams inside for objective grabbing.
Also, if you have them, infiltrating sentinels with autocannons can be fun, if not really effective, to grab some objectives, get linebreaker and harass enemy rearguard.
This said, IG is one of the worst codices out there at the moment, sadly. Expect no easy game and be prepared to get some prostate examinations by the average list of Eldar, Tau, Necron and Space Marines in general.

 

[neferhet]

Depending on the casual level: i've never lost to guard in casual games. Also, every casual game i've had playing guard was an uphill struggle. As far as i have seen, causal Tau-eldar-necron lists have a power level that is apalling. However, for casual/fun play any army is fine. Simply you will play in "hard" mode (being Orks and chaos marines the "very hard" :-D )
Ig is so bad right now because it has few and not so good (also nerfed) formations, while the above mentioned armies swell with powerful formations. I guess that if you stick with simple cad, just out of the codex, it wil even a bit the odds.