So, I've been playing 1.8 SSP for a few days now, and I have some thoughts. For those of you who haven't had a chance to update and play it yet, these might serve as spoilers. If not, continue reading.
First off, I think most of the changes are fantastic. The new, larger biomes give the game a much more epic world-feel in that they actually feel more like a biome and less like a "What the heck was that?" I've already run into a village and mineshaft, both, and while the villages are hardly exemplary in their current state, mineshafts are amazing! They're a great source of iron ores, coal, and other minerals depending on their depth, and if you're afraid you might be stuck in them for a while, you can typically scavenge enough wood to make more torches or gather bread for healing and survival from the various chests contained therein.
The new combined hunger and healing model is a huge improvement over the stuff-your-face-til-your-hearts-are-full approach of gameplay, particularly once you've descended into the bowels of the earth. It is now almost mandatory that you carry a ration of food on your person should your stay extend into Minecraft days--or weeks. Even on normal, it's possible that your hearts will be depleted if you begin to starve, although you only die on hard mode. Healing over time plus the well fed self-regeneration bonus are a nice touch. It certainly adds more tension to the game when you have to cower in a dark corner while stuffing your face in the hopes that you'll regain enough health to kill the remaining mobs ahead of you to press on.
I suspect, though, that I'm going to wind up playing the game in either creative or peaceful mode until further improvements are made. My reasoning is simple: Hostile mobs are too easy now, and peaceful mobs become increasingly difficult to find the longer you stay in any given zone. Most hostile mobs drop with two shots from the charged bow, and your new ability to block incoming attacks from zombies with the right-click parry function of the sword renders them laughably easy. Passive mobs spawn more rarely now making food difficult to find, and as you kill them it's feasible that they'll cycle out with squid rendering you chickenless, pigless, cowless, and all other kinds of -less except squidless (and good luck swimming to the bottom of the sea to kill the half dozen or more squid clustering together in a massive bottom-feeding orgy).
The biggest change that really did it in for me tonight was the change to creepers. Prior to 1.8, creepers made absolutely no indication of their suicidal presence until they were on top of you with their iconic "hiss." Now, everything that moves makes a shuffling sound, including creepers. This absolutely destroys the fear of running around at night, because you can almost always hear a creeper well before it sees you, and definitely long before it's close enough to detonate. So far, I've only detonated a creeper once, and that's because I had my speakers muted. That's how ridiculous this is.
You may have noticed that I haven't mentioned Endermen yet. It's quite simple: They're not all that scary, and they're far more annoying than they are terrifying. My first encounter with one I angered intentionally ended quickly; it teleported up to me, and I ran inside only to find out that they can teleport indoors. Yes, I was indeed terrified when its gaping visage came charging toward me at lightning speed--with a block of grass in hand--and it nearly two-shotted me on normal difficulty. Yet, once I learned how to avoid them, they became less frightening and more of a nuisance. Now, as I wander the forests, I find missing tree trunks everywhere with the odd log, block of dirt, or leaf block placed in a bizarre spot. But the most annoying thing is that they neither place picked up blocks with regularity nor do they drop them upon death. It seems to me that the only thing Endermen excel at killing is the humble building block, which die off en masse alongside their captors at the rising of the sun. Left behind is a swathe of pockmarked terrain and trunkless trees that would drive anyone with even the slightest leanings toward OCD mad.
I'll be playing on peaceful from now on, because the hostile mobs are hardly all that dangerous anymore. Passive mobs spawn with such irregularity thanks to the animal husbandry code being absent (currently), although that's slated to be fixed; I just hope the game becomes a little more like the way it was when you were actually terrified to go outside your front door for fear of being blown to smithereens (and having your house reduced to a pile of rubble, too).