You made a comment about there been no footslogging IG lists anymore...not true at all. There's always some popping up in the armylists Forum, plus I know a few guys on here who field them all the time, plus all 12/15 regulars I play against (me included) can and do field Infantry-heavy lists.
No, I was referring to what 4th Ed. Dual Lash CSM did to the meta, and why there's rarely any foot lists anymore because such a list still exists.
Let me open up the discussion with a more argumentative description.
Mech Guard is very competitive, and in my opinion, the most competitive army in 40K right now. It completely changes the metagame and dominates what type of army lists are fielded in most tournaments. If you've ever played in a tournament, you normally design your army list to fight a certain metagame. The current 5th Ed. Metagame is (and this is a brief layout): TWC Wolves, RB Spam Wolf or Angels, Mech Guard, Dual Lash and insert some random local metagame stuff here.
Do I think Guard is a good book? Yes and No. Yes in the fact that it can make the most min-maxed options that kick ass in a certain meta, and no because more than half the book is crap. The reason is because Guard has a lot of options but not many of them are good. The good ones, however, are underpriced, have great stats and you can field a lot of them.
Could this be what GW intended? Probably not. But who cares, the average cost of a 2000 Mech Guard army is up the roof and people will buy X netlist from X discount retailer and roll face all day. I have played with and against Mech Guard. I have tasted the IG codex and I'm not impressed. I'm impressed by the power that it produces, but I'm not impressed with the simplicity it takes to play a army that can shoot well, deliver crushing and powerful salvos turn after turn, and remain relatively safe behind their AV12+ wall.
Back in 4th I saw a lot of foot Guard lists with a relatively few number of tanks. Maybe like 4-5. Only the Steel Legion players spammed their Chimeras and even so, it was within the sanity boundaries because you can only field so many of them. Now, everything got a discount and Veterans with BS4 were made troops. Vendettas and Valks are also extremely good for the points and Marbo for 65 points makes Lictors look like mental defuncts.
The list goes on, but it goes without saying that competitive IG (not IG as a whole) is an extremely powerful book. Now for those players who remember the days where Nidzilla and Lash shaped the metagame, I dare you guys to argue differently. 5th Ed. Mech Guard has changed the metagame more so than any other book I've seen thus far. They've also set the tone for the current edition and that's if you want to win, you bring equal or greater firepower or lose and die. This is the trend I'm seeing in 5th Ed. and it's not going to change in the near future.
Keep this going please, but with slightly greater and more elaborate refutes.