I think that your first impression will probably hold throughout your Trailblazer experience. There did not seem to be anything that became more broken in Trailblazer. Though, there are still discrepancies (as you mentioned) between caster and non caster classes power and versatility.
The biggest problem that I've seen has been the, "Its just like 3.5, except" problem, which is true of any incremental system update. To better explain what I mean, The rules for Trailblazer are very similar (even identical to) D&D 3.5 in most instances, except where they made (sometimes a very small) a change, so remembering where the system operates like 3.5 and where it operates differently can sometimes cause confusion.
Having not been as familiar with 3.5, you may not experience this. Also, depending on how much your group looks at the actual text of the rules in play, you may or may not even notice.
I have also not had any experience with the unified casting system regarding multiclassing. I think its just that our group has it so ingrained not to multiclass that no one has been brave enough to try it out yet.