I'm just not seeing Ring of Fire as a great ability to get 1 point in, early on. It's a GOOD ability, but it's fairly expensive on mana for little damage. It works vs newer/unsure players as a deterent, but even at high level, it doesn't put out the damage. Maxed out at 1500 dmg, that's still over 10 secs and is helpful, but I'm having fairly good luck skipping Ring of Fire and using the points into frost nova.
Not sure what it looks like on paper, but it works well in game. Fire Nova takes care of my higher level creeping (priests, etc) that would take longer, but generally, getting +50% dmg on form change is enough at low levels to do the deed quick.
Frost nova is pretty damn useful, whether for running or chasing. Fire build TB is very quick. If you need to run, freeze them and the slow after affect will pretty much save your bacon. Chasing, if you can catch up enough, freeze and then your teammates are on him, and he's slowed. Level 15 freeze is golden, with 3 secs frozen and -40% (I think?) slow. They're screwed. And it's an interrupt vs scrolls or long potions.
Ring of Fire is a low level aid. It may even be worth keeping lvl 1 in it for easy creeping, but I really feel like it's wasted, when at low levels, TB has so many options to pick that would do better.
BTW, I don't think deep freeze is worth getting. The extra fireball damage is nice, but all those points wasted! And it takes away the debuffs. If I slow an enemy 40%, I don't want to trade that for 375 dmg! I can rack up 375 in 2 hits, which I'll get on the slowed DG, plus many more.
Deep Freeze... it looks great, but I'm just not seeing it useful at low levels. It, imho, just causes a retreat to a tower until they're abilities are up again. Small victory, but takes mana and doesn't bring the pain enough.
Thoughts?