When attempting to think of DT's weakest album (and none of them can really be described in any way as "weak", The albums that come to most DT fan's minds are this album and Falling Into Infinity. While the latter is considered less stellar due to a few more commercialized songs, and a lot of fans' disdain for Derek Sherinian, When Dream and Day Unite has neither of those "problems".
The main problem that I have with this album is the production, the album was rushed and was put out on a very low budget, and it was also recorded on analog equipment, which has inperfections that translate to CD. The songs on it are wonderful, but they don't always sound great in terms of sound-quality.
The linup of this album is unique to this album only, as singer Charlie Dominici was fired after it's release. While it's certainly unanimous that Charlie's vocal's are the weak link in the band at this point, that's not to say they're horrible, or even bad. The man certainly can sing, however his range doesn't really include the higher-pitched notes that he's forced to hit on these songs. While we would all enjoy a remake of this album with James LaBrie singing, I personally think that the album would benefit MORE from better production than from switching singers.
The sound of this album has been described as a mixture of Journey, Rush, Metallica and Queensryche. This would be accurate. The album also has a heavy 80's vibe to it, which might turn off people unfamiliar with DT. I wouldn't reccomend this as a first purchase, as people who hear this album first might disregard DT as being a hair-metal band. Barring production, I would say I enjoy this album moreso than Falling into Infintiy, as there's not a single song on this album i dislike (maybe becuase there's only 8 songs though!) The albm clocks in at a little over 50 minutes, which is short by today's standards, but you have to remember that this being 1987, the album was also released on cassette and vinyl record. The highlights of this album are the soaring epic The Killing Hand. the fast-paced Only A Matter of Time. and the complex instrumental Ytse Jam.
DT's love for longer songs isn't fully realized on this album, as four songs are less than 6 minutes long, and the longest song on the album is only 8:42 (this is less than dream theater's average of 8:55), however the progness of these songs never comes into doubt.
In short, if you're a DT fan/collector, you need to have this album. You'll probably want the limited edition digi-pack if you are a collector, but I heartily reccomend the jewel case edition as you get more pictures with it, and full lyrics. Casual DT listeners will want to hear this one before they buy it, and I think it should never be your first purchase.