HackMaster 5e is an amazing game. Here is a review I did for rpg.net that covers (in detail) my perceived positives and negatives of the game. I hope you decide to give it a try.
I have read numerous posts over the different forums of people converting over to Hackmaster because of the combat system alone. Combat just makes sense from the beginning to the end.
Having enjoyed reading (but sadly never able to get a game together) of Hackmaster 4e, I bought the 5e players book sight unseen.
I've never regretted the purchase. Read David's review because he covers most of it quite well. I would note that the the "overconfidence" mentioned is a product of the rulebook being "written" by the designers at "Hard Eight" enterprises, the same fictional company that wrote Hackmaster 4e. The humor of H4e is still there and it pops up from time to time, but it is toned way, way down. Make no mistake, though. The humor does not detract from the game, it is a serious and well-written product.
For anyone interested, download the free basic game at the KenzerCo web site, or pop for the $10 pdf of the Basic Plus (which is enough to get a good, deeper impression of what Hackmaster can do).
As for the 5e hardback, it is on the pricey side, but it is a gorgeous book, extremely well made and in my mind worth every penny.
Happy Hacking!