In Which I Run 5E... and a TPK nearly happens

Last night, I ran my wife and some friends through the beginning of the 5E adventure, the Lost Mine of Phandelver, using four of the five pre-made characters. They group made it through the first encounter with the goblin skirmishers okay, but once they got to the caves, things went south in a hurry. The fighter (after successful scouting by the halfling rogue) decided to try and sneak up to take out the goblin guarding the bridge. A failed stealth check and two failed attack rolls later, and he had sounded an alarm (I sort of improvised that, but it made sense. If you've got a guard on watch, he should have a shell to blow into or something to warn the others), and the whole place was emptying on them. They had befriended the wolves, but that didn't matter much once the bugbear riled them up into a frenzy, and they couldn't navigate too much farther in once the flood washed the fighter out and sent her all the way back to the opening. Goblin archers quickly cut down the rogue and the magic user, and the dwarf cleric and fighter had to grab the two and run. They got away, but didn't really get much out of the adventure other than riling up the goblins and making sure they have posted extra guards the next time they come back...

A few takeaways:

- I asked once if they were going to rest after the battle with the skirmishers on the road, and they said no - they felt good about themselves. That was a big mistake. They didn't try to conserve resources (especially spells) and were left with no healing and no heavy hitting spells when it mattered, because they had been all in from the get go. In my Splintered Realm play testing, they've all been running around with level 5 characters, and are used to having more resources at their disposal.
- I like this game quite a bit, although I still like the rules I'm developing better (I should hope so! I'm writing them!). I feel like some of the fiddly bits are a little too fiddly for my taste... I especially don't like that a 6 point difference in ability scores translates (assuming no other factors) into a 15% difference in many situations. A character with STR 17 has a 15% better chance of making a STR check than a character with STR 10. That's a small gain, on the whole, for a large disparity in ability scores. In Splintered Realm terms, that is the difference between a STR 11 and STR 6, which is still only a 25% difference on a check, but that 10% feels like a big difference to me. The character sheet really shows how unimportant ability scores are; since that's the case, why are the scores even there? Just get rid of them altogether...
- I know that advantage/disadvantage is all the rage right now, but I just don't see it as vastly superior to a situational modifier. I didn't feel the need to adapt this for Splintered Realm. I figure that if other people love it, they can always plug it in as a house rule without much effort. For me, meh.
- I don't like the escalation of numbers for no good reason. Why does magic missile deal 3d4+3 damage? Because an average hobgoblin has 11 hit points, that's why... Can't your average hobgoblin just still have 5 hit points like in 'the old days' and then your magic missile can do about 5 points... it feels like there's a bit of a shell game with escalation of numbers. It's fine, I just don't see the need for it. You can scale the numbers back and make the whole thing easier to track.
- I can't wrap my head around 'spending' hit dice to get healing during a short rest. You aren't 'spending' anything. Right? Is this defining 'hit dice' as an ability specifically set aside for self healing and not for determining hit points? I can't find that in the rules anywhere...
- Death saves came into play for two characters. This was an okay mechanic... I'm pretty neutral on it.
- Another apples/oranges thing, but I don't like the idea of shifting DCs the way they are implemented here. I'd rather have the difficulty set and modifiers to the roll. That's probably just me. I also think that a target of 10 is too low (an untrained person with no ability at all can do this 50% of the time), because it's almost not worth rolling - heroic characters should just be able to do such things.