Busy weekend caused me to miss my Musical Discoveries post, but instead of posting late I've decided to postpone to next week and prioritize continuing this; I keep putting it off because of how long it takes, but at this point it's getting past the point of acceptability.
I could probably fill a thread of its own with original Zunish compositions, a good portion of which would be from fangames (but instead I occasionally feature them in the MD thread). I won't do entries like yours just yet, but I may consider doing so later on.
Now, for the first modern era!
Actually, where does this era start for the music collections? Should I have included music collections four and five in the classic era? Well, too late now.
ZUN's Music Collection Vol. 4: Retrospective 53 Minutes
Easy picks, and fitting openers as well. Hiroshige No.36 ~ Neo Super-Express and Blue Sea of 53 Minutes are hard to beat, both for their superior atmosphere and complimentary usage of ambient sound effects. They also do a good job at showcases the distinct sound that music collection originals tend to have; Neo Super-Express would need some tweaking to pass as a stage theme, but Blue Sea would require a complete overhaul (which has been done, but the point stands).
ZUN's Music Collection Vol. 5: Magical Astronomy
By far my favorite music collection volume, featuring a healthily limited quantity of remixes (that are nonetheless noteworthy among their kind) and several originals of legendary arrangement. G-Free is one of those tracks vying for the mysterious #11 spot in my ranking, capturing all the intensity of a boss theme while also carrying the spacey style that characterizes this album. Beyond that, it's almost impossible to pick a track out from the collection. Obviously Greenwich in the Sky gets plenty of love, but Satellite Cafe Terrace and Welcome to the Moon Tour deserve at least as much attention. So for this one I'll cheat and leave it open; if pressed, I'll favour the latter two for second spot and honorable mention, respectively.
Perfect Memento in Strict Sense
This is another tiny three-track EP, but where the previous example was somewhat forgettable, this one is worth giving some time to. It is one of two entries where ZUN experimented with his old PC-98 sounds, unrestrained by the confines of their native hardware. All three are noteworthy arrangements; especially relevant is Child of Are, the official theme of written-work-exclusive character Akyuu (keep in mind that this was released around the same time as the Untouched Scores series was coming out). The collection is characterized by an almost off-key sounding harmonization structure, feeling conflicted but somehow cohesive. I think my personal favorite is Japanese Saga, but hopefully all three will receive proper appreciation.
Technically Eastern and Little Nature Deity would be next, but I'm skipping it for reasons that will be stated shortly.
Touhou 10 ~ Mountain of Faith
Earlier I referred to this soundtrack as having "overall strength" in comparison to other entries. By this I meant that there is a standard of quality motifs and progression structures that persists throughout the soundtrack; as a complete collection, I would consider it my favorite in the series. Everything said about Music Collection 5 applies here; Gensokyo Beloved is easily my favorite track (for reasons given elsewhere), but beyond that becomes a difficult choice. For now, I shall go with Faith is for the Transient People, and add Fall of Fall ~ Autumn Waterfall as honorable mention.
Strange and Bright Nature Deity
The music for this series of written works was spread across three separate releases, all of which could accurately be called EPs. Given that they all follow the same story, and are even named the same with successive numbering, I am considering them as a single collection. Additionally, the tracks from Eastern and Little Nature Deity were re-released as part of this series with little change, so I am grouping that into the collection as well.
I ought to admit to being less familiar with these tracks than usual; in fact, you may consider the Three Faries my "blind-spot" for Touhou music. I can safely say that Sunny Rutile Flection is my favorite of the three character themes (as well as one of the strangest names for a track I know of in a series full of odd titles), and I can easily recommend the rest of the collection based upon my vague memory of them, but it may be unfair of me to pick a secondary favorite. The one other track that stands out to me is the collection's rendition of The Refrain of the Lovely Great War; it predated the game it would later be remixed for, and I personally prefer this older version by a great deal.
That isn't very much ground covered, but it's been an hour and I'm out of time. Have patience; Lord willing, I shall return!