Skill and stat points are make and break it in TL II. D3 has enormous amount of hand-holding here: stats are allocated automatically, and skill system is pretty dull. You can slightly improve skills with runes (which slightly improve effect of skill), by choosing one of 4-6 runes per skill, but most of those are boring and unimaginative. In example, Wizard's Magic Missile has only 1 cool rune choice - Seeking. And if rune happens to be interesting and drastically changing gameplay, it becomes subject to nerf in hotfix or patch.
In TL II, each skill has 15 levels and 3 tiers. Each skill level is "quantity" upgrade (skill's effect is increased), each skill tier is "quality" upgrade (skill gets additional effect/bonus). Respeccing in TL2 is tricky part, you will be able to easily reallocate only 3 last skill points, but it makes choice even moreso important and requires careful preplanning of character's build if want to do all high level challenges.
About D3. When you reach lv60, the only somewhat efficient way to move anywhere, is to get 5 Nephalem Valor stacks. It is special buff you get after killing 5 elite packs of mobs, and each time you relog/switch act, dc or whatever - you lose stacks. Those stacks give big bonuses to gold find, magic find and paragon exp, it is pointless to farm anything without those 5 stacks. It means you need minimum time to invest in gaming session, and you must grind those 5 stacks each time. It is fun only the first time, then it turns into tedium, with feeling of wasting time when you are running around without 5 stacks, and then locking you into grinding entire act in a single session for maximum output. You need to grind each time only to be able to start grinding, and if you go to make dinner or something like that - server will kick you for inactivity and you will have to start grind all over again.
Torchlight II - single player mode: your progress is saved each time you exit game. Each time you resume game, you will start from exactly same point where you were last time. Multiplayer mode: adds option to reroll world (applicable to single player too) or join game in progress of someone else. In comparison to D3, in D3 each time you relog or dc - all your exploration progress is lost forever and maps reset, even in single player mode. However, people have problems with Steam version of TL II due to Steam's notorious cloud-saving, if you will buy TL2 directly from Runic, you won't have any problems with that.