A little background, first: I have played D&D for more than 20 years in its different editions, with a group of friends and in a gaming club. I decided to DM HARP because 3.5 became too cumbersome and too heavy on my side, too many numbers and rules, not enough "play". Just my experience here, no flame intended.
-- Does it play faster and easier than D&D 3.5?
Yes, on the combat side, if you get a grasp of the spirit of the rules. Learning curve was step in our group. But now, we can handle a big fight with 5 or 6 NPCs opponents each with different classes in a breeze. Players have to know some rules. I DM with a laptop and use some tools to speed up play. Preparation time is much faster for me, it's easy to create a believable opponnent is a few minutes without going to a full blown PC charsheet. Spell casting can be a bit slow as you have a lot of options to take, but I use a tool there to do the calc, so I consider this as a rich part of the game. On the d100 side, adding 73 and 39 is slow for some of our players, so they let the others do the calc.
In the end, combat has become for me a richer experience, less based on meta gaming issues (squares, AoOs, etc.) gradually more cinematic and better described. After a game, I dont dream of squares but of the heroic deeds of my character or of the epic stories I'm helping my players build
-- Can you create characters much different from D&D archetypes (say, what about a fighter in HARP, as compared to a fighter in D&D)?
Yes, you can. All the things done by your char are skills, and you can add points to any skill you want (except magic, at least in my game), just having to pay single or double point cost. So in our group we have a Dwarf specialized in finding and preparing Herbs, a main caster which is in fact a Healer and uses a lot of "attack" spells (as healing is handled in part by the herbs), and an Elf who did some combo with the Rogue class at the start, ending with something like a stealthy magically enhanced fighter. It's also very easy to create your own classes, as the numbers are given in the rules and it's not much more than a choice of which skill categories are "favorites" and 3 special "class powers" easily defined.
-- Does magic feel really different?
Yes! Casters have a small number of spells at start, but can scale them up at the time of casting. This makes for interesting strategies at prep time (I need to put some ranks here so that I can scale more, not there because scaling is ok now, but as I want to cast fast and with an armor, I have to do it there also, but as this spell I can cast slowly not under stress conditions, 5 ranks are enough. What if I could make it last a bit longer...). And during the game, this also plays an important part for the players, as they have to make choices when casting, can fail, but can also crit.
-- In what setting do you use HARP?
Middle Earth 4th Age (see my sig).
-- Overall, do just the game mechanics change but it's still a fantasy world of elves, dwarves, fighters, clerics, and mages? Or does it really change the experience of play?
You're right, other mecanics, but same experience at the end. The switch to HARP made me re-consider my DMing style, adding more RP and NPC interaction and less fights, but I could have done this with D&D too.
-- any other question you may think of and want to answer?
I dont really agree on the "HARP magic fits better in a low magic setting": if you read College of Magics, the most excellent RPG supplement I have read in years, you find a lot of very good things to handle a high magic setting, and I think that the system is smooth enough to let you graduate at will on this side.
Edits were for spelling mainly.
