I did get a chance to do a little play testing recently when I converted my kids characters from Microlite to Beacon. At first they were mad because Beacon skills are not as generous as the Microlite ones. In Microlight you get a +1 to all skills every level but in Beacon you get class specific skill bumps every 3 or 5 levels and only get to choose one skill to do the +1 increase. They were pretty pissed I was messing with their d&d guys, which I gathered was as bad as messing with their webkinz, so I guess I should be happy they are that involved. Anyway after that was sorted out, we played and there was no problem with the slight increase in complexity. I did discover some holes in the rules that need plugging - such as a explaining ranged weapon increments in the rule book (turns out it works just like in the SRD). We didn't get into any of the fancier rules for terrain or combat but the critical hit and fumble table was a big success, especially when in the same fight they did double damage to a goblin (knocking him out a door and off a cliff ledge) and then another poor goblin broke his arm trying to stab the rogue (he rolled a 3 on 2d10). Good times.
I did spend some time again thinking that the Microlite convention of adding +1 to hit for every level might be too generous - or perhaps too generous for all classes anyway. It's a good mechanic because it's simple and it theoretically compensates for the lack of feats and powers that you would find in other d20 systems. But it certainly smooths out some of the differences in combat ability between the classes. I've had it in red in the draft rules for a while but I didn't know what I wanted to do with it. I could of course go with something where Fighters and Hunters (ranged) got +1 per level, Rogues and Hunters (melee) got +1 every 2 levels and the magic classes got +1 every 3 levels. Or perhaps Fighters get +1 per level, Hunters get +1/level for ranged weapons only, and all the other classes get +1 every 2 levels. It's simple and offsets the classes well, however I haven't done this because I am still wondering how if that would retard combat development when compared to the expected combat ability in published materials. I also wonder if I care. Slowing down the progression won't actually break compatibility - and using packaged materials in your campaign is something requires sanity checks in any case.