Used to play LoL a fair bit, and still watch it every once in a while, but have mostly switched over to Dota.
Major differences:
-No denying in LoL
-The lanes are much more rigid, with 1 top, 1 mid, 2 bottom, and 1 jungle being the standard meta, although in competitive you will sometimes see lane swaps. I can't say I've ever seen anything like an aggressive tri-lane in LoL.
-There's a lot more out of game but game impacting customization of your hero/champ in LoL that is tied into their micro transactions (runes) and account leveling (masteries).
In Dota all of these small differences are absent, and the items are generally more impactful and more frequently have actives. The biggest out of game impacts are from your choice of heroes.
-On that same note, in LoL, you only have a small roster of free champions each week, plus a couple of starter champions, to play from initially. You can buy more as you earn more in game currency or pay money to unlock them directly. This is contrasted with DOTA giving you all of the heroes up front as soon as you make your account, with only cosmetics being for sold for real money.
-Spells are generally more costly and less spammable in Dota versus LoL.
Champions in LoL are usually centered on one controllable unit, with some having a second unit that's controllable through an alt-click. This contrasts Dota's more RTS controls where heroes are capable of amassing armies of units.
-I'm sure I'm forgetting some things, but overall a lot comes down to the different design philosophies of either game. Valve strives with DOTA 2 for "perfect imbalance", with everything having some "overpowered" aspects. I can't really speak to what Riot's current design philosophy with LoL, as I haven't followed it a lot recently, but a lot of the decisions are built around their specific take on the f2p model.
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