1. Graphics and interface
This is the most immediate difference I noticed with LoL and HoN. Whereas LoL's graphics are of acceptable quality, HoN obviously takes Warcraft III's style and improves on it. The opening menu screen has superb artwork and the menu graphics are well designed and pleasing to the eye. LoL on the other hand has minimal artwork and blocky, simple buttons and screens. Whereas LoL has buttons all over the screen, HoN's buttons seem to be located at more logical places, allowing the user to easier use the interface. It's a minor point that more experienced users will not care about, but I thought it was worth mentioning.
Overall, HoN's interface is beautiful, professional, and makes you enthusiastic about playing the game. LoL's interface is very underwhelming in comparison.
HoN is also much better during character selection. In HoN, each hero's abilities and descriptions are displayed right there on the screen, while in LoL you have to click another button to see all the information. Again, not a problem for experienced players.
Character artwork in HoN is much better in my opinion. The artwork is more of a painting style that really adds to the darker and serious setting of HoN. LoL's artwork looks like it was done by different artists, each hero has a different body proportion, and overall any given hero looks out of place when standing next to another hero.
In-game graphics are also extremely different. As before, HoN models its style after WCIII and Dota, even giving the creeps a similiar look. Textures and models are better than LoL, but I found that there was less character detail than LoL, and LoL had smoother animation. HoN's animation seemed jerky and blocky at times, while LoL's animations have always been smooth.
In HoN, many of your hero's stats are displayed right there on the screen, without having to click on your hero portrait to know everything.
When I heard the HoN was a direct copy of DOTA, I never really knew how true that statement was. Almost every single element from DOTA was reproduced in HoN, straight down to the "xxxx pwned xxxx's head for 215 gold!" messages.
Item selections in HoN is again straight out of DOTA. Unlike LoL, HoN has no "suggested items" making it difficult for newer players to try out heroes and items. LoL has a better Item selection screen, easily breaking down item categories that make it easy to buy what you're looking for. HoN on the other hand borrows the same clunky item selection and recipe formation from DOTA.
Gameplay in HoN is exactly the same as DOTA. Go to a lane, last hit and deny, gank at mid lvl, push at end game. LoL on the other hand has no deny system, making hero to hero combat more important, and ultimately makes the beginning of the game more enjoyable. Instead of spending 15 minutes last hitting and denying trying to keep creeps towards your side in HoN, LoL rewards you for being offensive.
Heroes from HoN are again almost direct ports from DOTA. They are so similiar, players in HoN were calling their hero's by their DOTA name instead of the HoN name, because they were directly transferable.
HoN again borrows the stat system from DOTA, while LoL takes a differenct approach, not tying your hero down to a certain stat build. As in DOTA, in HoN if you have an agility hero you stack agility, strength heroes stack strength, etc. In LoL you are much more free in your build.
Overall, just looking at the 2 games, my personal opinion is that LoL will ultimately be the better game. HoN has shown that their developers lack any vision or ingenuity, and I doubt they can progress any further than their initial release. LoL has many newer, better ideas for the direction of DOTA-like games, and I believe the future lies with LoL. The only thing holding back LoL from widespread success is the cartoony style andgraphics that many, MANY, experienced gamers will immedietely dislike.