If you're looking for a fresh DotA-like game look no further. I should re-highlight that non-paying gamers will in...
PROS: Similar in spirit to DotA, with a few additional features such as Match-making and more maps (currently only 2 though =( ). Game is completely free and a non-payer can achieve everything a payer can, albeit with a little more effort.
CONS: Gameplay might differ from DotA: not allowed to deny creeps or towers, no bashers item (which is actaully a gd thing).
League of Legends is a game made by guinsoo, one of the designers of DotA (before Icefrog). DotA players will be at ease playing this as it is at its core very similar to DotA. It does have many additional features which makes it a strong competitor to DotA.
The summoner
The first difference you'll notice is that you are a "summoner" which can gain levels. This adds a persistent RPG aspect to the game. As you play more games, your summoner gains both XP(experience) to level up and IP(influence points) the in-game currency to unlock more heros and runes. Everytime you level up you gain mastery points which similar to WOW can be used to specialise your heros by giving it slight perks (increase in physical damage, less skill cooldown, etc...). These benefits aren't game breaking, making it very possible for a skilled lower level summoner without much mastery points or runes to defeat a higher level summoner. What are runes? Runes are purchased
using IP and boasts your heros in the same way as masteries.
Matchmaking
You begin a match by joining the queue which is roughly under a min. The game match-making system finds similarly skilled players so you can expect a challenging match most of the time. You can also play with friends in a premade. The game has a buddy list and chat all build-in so it's convenient to organise a match with friends.
Hero selection
Once you've been placed in a team, you (and your teammates) will have 90 secs to choose your hero, runes and summoner spells. Summoner spells are spells separate from the ones your heros have. These summoner spells are mainly utility, one such as flash (blink with a long cooldown) and immunity to your towers for a short duration. These spells allow for further customisation of your play style. Do you want to have an escape mechanism or a short debuff to slow your enemy? You will be able to see your teammates selections so you can choose a hero to complement your team. Your enemies heros selection will be hidden though, so you can't pick heros to counter your opponents' ones. Another thing about heros selection is that you can only pick heros that have been unlocked. There will be a new set of 8 heros unlocked every week for free so you can always try them before buying. Some heros are cheap to get and can be easily bought using the IP earned after 5 matches, others can take a painful amount of IP.
Match start
Once the hero selection is completed, the programme proceeds to the loading screen and then the game begins. The interface should looks familar to DotA players. One of the first thing you'll notice is that there is only one shop at your fountain. The items purchasable in LoL are categorise according to their function. This can take a while to get used to but is ultimately a much slicker system compared to DotA. One popular item missing in LoL is the teleport scroll. All champions can teleport back to base anytime, anywhere, after an 8 secs channeling spell with no cd. Teleporting away from base can only be done using the summoner spell: teleport. Don't know which items to get for your hero? Every hero has 6 recommended item viewable at the shop.
Terrain / Map
The terrain of the main LoL map has a similar layout with neutral creeps camps and also Roshan's cousin: Nashor (an anagram of 'roshan'). LoL also adds the 'bush/long grass' element into the terrain. Those terrain type will hide any hero in it unless the enemy's hero enter the bush too. Often used for tactical ambushes or juking. Netreul creeps such as the lizard and golem confer a special buff upon the hero who kills them. These temporary buffs are highly sought after and can power up your heros significantly, giving increased damage, mana regen, reduced skill cooldown. The mini map shows the faces of the heros for easy tracking of heros instead of just the colour coding in DotA.
Combat
You will notice that the hotkey for using the hero's skills has been allocated to 'Q','W','E','R' by default remove the akward finger placement some DotA heros require. Items use are also defaulted to number 1-6 above 'Q', within easy reach of the left hand. A cool feature in LoL is the ability to mark an enemy player, doing so will place a cross-hair icon on the enemy hero. Great for telling your ally which hero you'll be aiming in a fight. The health bar displayed above each hero also visually tells you how much hp a hero has. Every block on the hp bar represents 100 hp, so you can tell a hero's hp in a quick glance.
If you're looking for a fresh DotA-like game look no further. I should re-highlight that non-paying gamers will in no way be disadvantaged in matches against paying gamers. Although, you should buy a custom hero skin or two to support the game developers. Imagine the awe and fear in your enemies' eyes when they see your custom skinned hero. "OMG, he/she spent cash on LoL, he must be some serious gamer, better not mess with him." *Runs away in fear* Ok, maybe that won't happen but you get the point.
To start, you can sign up here: https://signup.leagueoflegends.com?ref=4b4f192d09689. The referral at the end will net me some extra IP which is always a gd thing =). You could add me in game (Porcupine) if you have some questions on the game mechanics and I'll help to the best of my ability.
Have a LoLing gd time!