I actually worked in KPMG until recently and generally KPMG has taken a bit of a dip of late. They were never leading the big 4, usually hovering around 3rd. That has changed recently as there have been a number of leavers as KPMG struggles to understand which path it should take...more technology focus (but don't want to invest or take the risk), more high end experience consulting (but risk competing in areas they have little experience).
Consequently the partners are confused, not focused and operate in a very tactical and expedient manner. So it isn't great, but that said I would say the other big 4 are in similar positions as they grapple with having Audit functions and providing consulting advice. It would be handy to get on your CV for experience good brand etc, but I would think next step if I were you, which you should be doing anyway. Seems to me that Deloitte and PWC are doing ok (although they yo-yo in terms of recruitment and lay offs) EY are investing heavily in MC - KPMG are lagging as Deloitte are the the biggest followed by PWC...3rd if up for grabs but whoever it is, is a distant 3rd.
Specifically in terms of your query though;
Progression - you can expect to get promoted to D grade in 3 years, unless you fail exams or crash and burn or annoy a Partner.
Culture - good culture although my experience is that KPMG tend to sweat their staff more rather than Deloitte or PWC (i.e. KPMG have fewer people but same aspirations). The people are very friendly much more so than Deloitte, slightly flatter structure but Partners are Partners wherever you go.
Pay - I only think it is consistent with the other big 4, you do get a bonus though, but of course when times are bad, and they have been, the bonus gets canned.
Training - It has got better but most of what you learn will be on the job training.
Which area were you considering in KPMG MC?