We use armour adjustment with Martial Law criticals but not on-the-fly, we use a spreadsheet that does the adjustments for us in combat. The armour-lite characters do not like the adjustments that much but in general it seems a good system. We discussed shortly on the adjustment rules with metal armour and lightning bolts.
There has, however, also at several situations been talk about reintroducing RM2 combat system with its critical tables in order to add a (subjectively-felt) higher chance for deadly critical even with smaller weapons and a higher diversity of criticals afflicted. The problem with good fighters is that they get the high results too often and therefore get bored by them.
I think my players would like the A to E critical division more than the location specific ones as you could always add the location by just describing it but you get to hear more criticals in a combat than as is at the moment. (See the paragraph before.)
On the other hand, I have to tell that when we played RoleMaster 2nd Edition back then the fighters usually got frustrated with not being able to kill their enemies quickly despite having a high skill because of low critical rolls. Also the berserk always got knocked down because of his enemy's high critical rolls.
Back then we tried to find a solution which would allow a one roll attack solution. And now the feeling is just the opposite.
Personally, I think the main reason is hearing the same criticals too often and having the feeling that the killing chances are too little. They on the one hand do not find it dangerous aneough when they attack and on the other hand very lethal when attacked. IMHO the RM2 combat system took more time and was based more on chance than on skill but that chance made people experience more excitement in combat situations.
As I like playing with a spreadsheet I already though about extending the critical tables with a crit for every number and would also buy an application for my netbook or an android phone in order to use it for the game.
With spreadsheets/apps one could even go so far as to incorporate clickable options to pick what you want and also you could add A to E criticals with locations if you like. You could also expand the critical tables - maybe devising a formula would be a good idea. A formula that bases the hits inflicted on the attack (roll) and a little bit of chance with more penalties with slashing weapons, more stun with crushing weapons, bleeding with puncture weapons, etc.
(Phew, sorry about the long post. Got carried away a bit.)