Back on topic, the (core) spells that worry me the most are:

1) Wish. The drawbacks seem harsh enough to prevent abuse (or even use...) in combat unless as a last resort, though using it to cast any other spell appears to be free. It's not in the basic set, we'll wait for the PHB to be certain how it works exactly. For now, it looks very versatile and powerful, but it's not the 3.5 equivalent. Potential problem: can a wizard spam Wish during downtime every few days? I wouldn't like that.

2) Gate. You can use Gate to call a creature from another plane, but you need to know its name, which appears to make it a plot-related function only, or at least that's the intent (I guess). The intent won't be enough if you can just learn convenient names with divinations. The basic set doesn't include any such divinations, but maybe that's something for the Bard. The biggest change is what happens once the creature appears: you don't control it (yay!), it acts as it sees fit. Now, combined with other spells, Gate might be used to control a creature, which is a huge deal since there's no HD cap and no saving throw. From the basic set, only Dominate Monster seems appropriate - a concentration spell which grants another save every time the creature takes damage, so I'm not sure how viable it will be in practice. In any case, Gate seems perfectly fine for now. More material published may or may not make it dangerous.

3) Time Stop. The spell ends if you affect another creature or somebody else's items, or if you move more than 1000 ft away. It looks like you can use it to self-buff, set traps by affecting the environment only, and finish by attacking or fleeing. It seems pretty defensive, and I believe its usefulness in offense will depend on the availability of other spells.

4) Rope Trick. I always thought that this spell + divinations were the most unbalancing spells in 3.5 core, because they allowed prepared casters to actually be prepared for everything, long before we got to demiplane-related shenanigans. Rope Trick isn't in the basic set, does anyone know if we should expect it in the PHB?

5) Divination. If you cast it more than once before a long rest, there's a cumulative 25% chance to get a random answer. Which prevents spamming the spell, which is wonderful.

I'm not worried about Ice Assassin, because I don't expect it to make a comeback. Ever. If anyone knows otherwise, please let us know.