straight up, compare the melodies and harmonic movement (not the lyrics, it's strictly how they wrote the music i'm talking about) on Haven to about any other record, but let's say Construct in particular, since it's an extremely stark comparison. Construct is bleak in comparison; they were tapping into some serious doom metal vibes on that one, though obviously their tempos stayed fast. listen to the way the music of "Uniformity" is formed: semitones backed with fifths, parallel movement in the keyboards with the guitars and bass, it's all extremely desolate and negative. throw on "The Wonders at Your Feet" and it's the exact opposite (an observation of the band's prowess across the entire mood spectrum!): electronica keyboard voices playing catchy, friendly melodies under happier guitar leads and harmonic choices. listen to what the guitars play in the verses (or maybe it's a pre-chorus) after the rhythm-section-keys-vocals part — total change in mood, but it's not depressing, bleak, or even neutral; it's still 'happier' even though the song got heavier and deeper (probably a feeling aided by Anders switching to the toms-heavy beat) compared to "Uniformity." this happens all over Haven.
of course it has unhappy songs, it wouldn't be a DT record without; but even those songs have 'happy' harmonic writing — check out 1:40ish of "At Loss for Words" and tell me the harmonic change under the keyboard melody is sad or even neutral despite the overall track having a mood best described as unhappy (and less happy than the rest of the record, compositionally speaking). this is what i'm talking about; even in the epic album ender that covers lots of emotional territory, it's still absolutely covered in that writing style, whereas a track like "Monochromatic Stains" completely avoids it in every single possible way. it's something intrinsic to Haven that i personally don't like very much, and it's cool that lots of people do. i don't need to OK every compositional move they make, but it doesn't mean i have to like them all either.
it's how they were composing at the time, and it held over a bit into Damage Done ("Cathode Ray Sunshine" would have easily fit on Haven) but DD has a much broader mood spectrum representation in comparison, which is part of why i like it a lot more.