Hackmaster is currently my favorite fantasy RPG system.
Here are the pro's and con's as I see it, hope this helps.
Pros
Fast paced combat (which by the way may seem clunky but plays better, faster and easier than it may read)
shield use and shield breakage (very fun, somewhat realistic and makes shields useful)
Knockbacks
Spell points
Count up initiative system, which has ruined most turned based games for me.
Very heoric! Fights are awesome and can often go bad or good in unexpected ways.
trauma checks.
A game of touch choices. You generally have to sacrifice something to be good at something. You will not have 4 16+ stats, you will not be specialized to +3 in your weapon and be awesome at all of your skills at the same time, you will be forced to choose what is important to your PC. If you like overpowered PC's (and many gamers do and there is nothing wrong with that) you will not like HMB.
Cons (oddly enough most of these are because this is the basic version of the game)
HMB is rules-lite. You will need to use some common sense and make judgement calls. Some gamers CANNOT do this, if you cannot, you will be frustrated. Since this is the BASIC version of the game you will be forced to come up with some rule stipulations.
Only 5 levels, though KODT does have rules up to 10 but if you don't buy the mag you would have to spend the money on that.
Lack of equipment and spells (again more are available in KODT and hackjournal)
Lack of classes (again more available in KODT and hackjournal)
surprise system. I love the way it works, what I don't like is that combat could be going on for 10 seconds without someone being able to act. While not entirely unrealistic they need rules (and probably will have them) to allow people to shake others into action or revise the initiative system somewhat. Not broken by any means but just a minor irritation sometimes at the start of combat.
Overall HMB is fantastic game. My advice if you are interested is to try it out with an experienced GM. The reason I say this is because the rules sometimes seem clunky or complicated but in actual play (once you get them down) they are not at all. It is a very, very good system.