Well, I can't think of anything new to say, other than my group has been playing it for 4 months now, and we plan on continuing to play it for several more months. Our background is old 3E players, primarily Castles and Crusades players, none of us played Hackmaster 4E (except maybe a newer player, I'll have to ask him), and my group of 6 players (7 as of tonight) range from like it well enough to keep playing to it being their new favorite system.
Personally I like it, but it is not my new most favorite system, but unlike most I am willing to run it and play it. I am also concerned that with Advanced it will become too rules heavy, but another thing I like about HM so far is that the rules are very "modular", meaning I have been able to ignore using whatever rules I have wanted to ignore, and it plays just fine, and I believe it will stay that way with Advanced.
Also realize with the "penetration" rules (exploding damage dice) that HM has tended to be much deadlier than typical D&D. So HM players really need to think about attacking creatures in this game. I have 11 dead PC's so far. Killed by boars, skeletons, bear, a Troll, and other things.
To give an example, the party was level 4, with one level 3, and we had 7 players that night as well, and thinking in D&D terms they said, "7 of us should be able to take on a troll." With that they attacked. 12 seconds later 3 were dead and the rest were hiding, shaking with terror, behind hidden doors that they had found earlier. They never hit the Troll, not once.
So if HM is approached as a "hack and slash" game, create a dozen or so characters per player ahead of time.
HM also has a "Honor" system that largely works like Fate or Luck points in other games, which can help prevent deaths, but eventually even Honor tends to run out. Or, like in the case of the Troll, simply does not do enough to prevent the inevitable.