Very addictive, if you've played HoN, this review may help you understand why LoL is superior.
Some background, I tried DOTA in the early days when it was still an unknown mod, it didn't take my fancy so I moved on. In the last year I tried HoN off and on and grudgingly gave LoL a try even though HoN had really put me off this game style.
The difference between HoN and LoL is night and day, and I'll base my comparisons on HoN for anyone else coming from that game to LoL.
1) Yes HoN has a better graphics engine and alot more attention to detail but there's one very important issue with the graphics of both of these games. HoN, while super pretty, is super distracting. The lighting is wrong, the colours can confuse the senses... it sucks to have an enemy player sneak up amongst the creeps simply because the graphics lull you into overlooking details when spells and things are going off all over the screen.
LoL is the exact opposite, it forces you to focus on the action you're involved in, and makes it very clear to the senses that something is happening to you, or about to.
It may sound kind of retarded, but when you play the two, it's a major difference that has a huge impact on pulling you into not the game, but the actual strategy.
2) HoN player base is absolute crap. DOTA 1337 nerds that log onto the newbie servers and abuse everyone trying to learn the game for not being 'pro'... how many games were wasted when some nerd started getting upset because someone new didn't know what to do, even when they asked for help. The fact that there is no tutorial mode doesn't help, and the advice some of these nerds have of "play a private game against on your own to learn"... you learn nothing that way.
LoL on the other hand has a very intelligent, and I emphasise the word INTELLIGENT tutorial you can run through to learn all the basics you need to.. not just about how to control the game, but about the basic concepts of strategy used in the game, what your objective is, WHY you shouldn't feed the enemy with easy kills.
INTELLIGENT.
Add to that the player base, again, is the opposite of HoN. You don't have to rely on making your friends log in to play a private game to have fun (which you do on HoN if you want a whine free match)... Play on the servers appropriate to your skill, ask for help when you need it and LoL players are amazingly friendly. My experience in this area has been night and day.
HoN player base made me want to stop gaming online altogther, that's how repulsive those trolls are
LoL player base reminded me why multiplay is so much more fun than singleplay gaming.
3) HoN has a bunch of heroes all ready to play, even though the game is still (STILL) in beta.
LoL has a small amount of champions, but is growing... and is not still in beta.
LoL champions are being given more thought, are better balanced (to avoid 1337 spamming/exploiting... as much as is possible).
4) LoL is free to play.. you can pay for some extra features, but ultimately you can enjoy the game for free.
HoN, if it ever comes out of beta, will not be free to play... and why would you want to pay to play in a community of whiney children that spend all day playing a game they claim is "crap compared to DOTA"???
5) and lastly, Gamespot gave it a 6/10... Gamespot gave Napoleon Total War a glowing 8.5, and other such baffling hype-friendly reviews
LoL ain't cutting edge in the graphics engine driving it, and it's not pretending to be some revolutionary step in game mechanics.
LoL is in your face about what it's trying to achieve... a fun game. A game that feels fun, looks fun, is fun.
And it's a real game, not some self important interactive movie that is trying to advance the reputation of games onto the level of cinema, or any other pretentious ideal.
It's a GAME, and a damned good one at that, made by some indepedent dudes that are getting it right where so many massive budget developers are getting only half-right at the best of times. Support good game development, support this game by at least giving it a try... it's free after all.