Imperial Guard will have a hard time not having a lot of infantry or tanks in their army. Whilst it is obviously easy to forego tanks, your infantry numbers are often going to be high, even when you have 15+ tanks at any given points level. This combination of high infantry and tank numbers is often a problem for your opponent who cannot effectively deal with both aspects of the army at the same time. Whilst Imperial Guardsmen are pretty weak (T3/5+), having a bunch of them in cover (and combine with Go to Ground and Get Back Into the Fight!~) and essentially acting as ablative wounds for heavy or special weapons means shooting at them often doesn't do much to impact upon the game in the short-run.
What this basically boils down to is Imperial Guard can make the 'ultimate' hybrid list with many infantry models (approaching 100+) and many tanks (12-15+). Add in the firepower available to Imperial Guard armies and not only do you have a lot of damaging capacity, you also have a lot of ability to take fire and still run an effective list. What's great about this concept is the infantry don't all have to be in tanks which allows you freedom of deployment and movement. Obviously units like meltavets prefer to ride around in their Chimeras, maximising their threat ranges and survivability but Infantry Platoons and Heavy Weapon Teams can operate just as effectively outside their armored hulls. This can leave you vulnerable to your opponent's early shooting (everything has a target) but is also very likely to overwhelm your opponent with targets.
Imperial Guard are also one of the best scalers in the game. At every points level there are units which you can use and combine effectively starting from the mediocre 1500 scaling up through the lovely point ranges of 1750-2000 and maxing out somewhere around 10,000... What this means in practice is you have a ton of options available to you at your standard point values and whilst some units are more common there others, there are always choices to be made. When you expand outside of this points range, you still have a ton of options which some armies cannot claim.
So, when we put this all together with what we've discussed before and we have a very good army. I certainly think it's one of the better armies out there though I do feel the Internet gives it too much weight. Whether this stems from playing on boards without enough cover, always losing the first turn to leafblower type lists and not reserving, poor target priority or what, the Internet thinks IG are godly. They are certainly good and in the right hands, firing at AV12 for most of the game can be annoying. But they do have weaknesses. There are a lot of opportunity costs in their army. This comes from having a lot of choices and is no more apparent when balancing their firepower. They aren't the most mobile of armies and armies which can exploit this and get quick and plentiful AV10 side shots on Chimeras can make the mobile aspect of the Guard army come crashing down.
If you try and win a war of shooting attrition with Imperial Guard, you're often going to lose. They have too many options in this regard and plenty of units with which to threaten you with. This means you're going to have to out-manoeuvre and most likely out assault your opponent. Manuerving is obviously going to help setup side shots which is going to certainly help your army in terms of offensive potential but it also needs to limit the Guard mobility as well. If they are able to control midfield with a lot of Chimeras + Infantry, it's a lot harder to assault their bubble-wraps or parking lots in the backfield which put out a lot of firepower.
As an Imperial Guard player you obviously don't want this to happen and this is where your own movement and army construction comes into play. The more Chimeras you have moving into midfield, the longer you can keep that AV12 wall going. At the same time, the faster you move them and the more eager you are to get their meltagun infantry into range, the easier a time your opponent is going to have in getting side shots. Whilst this is happening your backline is vulnerable to disruption (deep-strike, outflanking, behind enemy lines, etc.) and you need to ensure your firepower isn't split between ranged S7 + blasts and short-ranged meltaguns.
In the end, when you can get the most out of the Imperial Guard codex you will have an extremely difficult army to beat with lots of tanks and infantry, high average AV on the front and a plethora of shooting options. Maximise these abilities and you are more likely to win but if your opponent is able to circumvent these or neutralise them, you are more likely to lose.
