Bull's Strength etc.: 1 min/level
IMO that's OK...
A good change. The spell is now set up to basically last for a single encounter, giving a decent boost for the duration of that encounter.
Longstride: 1h/level
A bit strong for a first level spell...
10 feet of movement isn't that amazing, and the classes that get it are fairly restricted.
Sleep: up to 4 HD
Was 2d4 overpowered? Wouldn't have thought so...
Sleep was THE low level combat spell all through 1st, 2nd and 3rd edition, and typically left the fighters of a group with absolutely nothing to do. 4HD means it's still a good spell, but not a dominating one.
Invisibility: 1min/level
Pretty short!
Let's take a look at some scenarios:
1. Rogue goes scouting on his own - he can't go too far from the rest of the group, because there is always a chance he'll be seen or heard and need backup. The party as a whole is involved in the adventure, and additionally the rogue gets some mileage out of his hard-earnt skill ranks.
2. Wizard casts invisibility (old version - 10 minutes a level) and goes scouting on his own - While the invisibility runs, the wizard has basically got no chance of being seen. He can go way ahead with minimal risk. The party basically may as well not be there. The result is that the wizard gets to do a lot of stuff for a long time, and everyone else just sits and watches. Additionally, the rogue may as well just pack it in as a scout.
3. Wizard casts invisibility (new version). Lasts for a minute a level, so the wizard has to stay close to the party. He still has no chance of being seen, but he can't go on such huge extended scouting missions any more. The rogue still loses a lot of power, but at least he's superior for long scouting missions.
Scorching Ray: 4d6 and it scales! Wow, wouldn't wanna miss that one!
Woohoo! A decent 2nd level damage spell! I don't think the problem is that it's too powerful - I think that the 2nd level damage spells (apart from it) are much too weak.
Darkness: I better skip that!
Bad writing means that it lights up areas. Apart from that I think it's a much better spell.
The old spell was awful - it basically 100% shut down any fight, and counters to it were few and far between.
Heaven forbid you met a juvenile black dragon - his blindsight and breath weapon combined with his darkness power basically meant that he'd TPK anyone unless you had daylight memorised or were immune to acid.