Think about it, LameDuke doesn't have any slopes and the final Derelict has very few. The 0.99 Beta has a few (Such as in the church in E1L3) that aren't in the final suggesting they went nuts with it when it was first implemented.
Blood is rather complicated, I am not sure I should post links to the Alpha for you to go and dig through it yourself as it may violate forum policies and I am still prohibited from sending PMs (Can this not be changed?) - Blood Wiki has a page on the Alpha at least
If you can get your hands on it there is some documentation included for XSystem (What I called QSystem before, handles Effects), QAV (Animated tiles - they are a single tile in Build/Artedit, a bit like Smacker), Smacker support for cutscenes (May not be with the Alpha, but the final used this) and all manner of things as well as a lot of maps.
One small paragraph;
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XSectors, XWalls, and XSprites
The XSystem is based on extending the three simple object types used in the Build engine: sectors, walls, and sprites. The extensions to these are referred to as XSectors, XWalls, and XSprites, or collectively as XObjects. Internally, the XSystem manages a list of each of each XObject and maintains links between its related object. The links are stored in the extra field, which you cannot edit in MapEdit, but can view with the Tab key in 2D mode.
Apparently this thing does use existing properties in Build then (Note, uses the Extra field to store "links") but allowed very complex control over things, for example what I remember (From the final, Alpha is a little less complex) is, you can set a Sector Type - ALT+F5 (ALT+F6 for sprites), maybe a Sliding Sector. That sector could move on it's own (Slide Sector) or else you could press K on a wall or sprite (Makes it purple) to affect that if it was inside that sector (Slide Marked) and hitting K again would reverse the direction for that one (Green).
Tags were instead TxID and RxID (F10 to find next free, first 100 reserved), Transmit and Recieve on different tags, you can select what triggers them/responds to them, different speed, waveforms and delays for On and Off, different starting state. Can set height for Z Motion Sector/Sprite (F3/F4. F2 to change current state). Can change how the player triggers any of these (Set switches to only respond to guns or whatever) and a lighting/panning system so you can make any sector flicker, fade or whatever in different waveforms, panning acts like Conveyers and can drag the player if the Drag box is ticked.
The RoR system deserves a mention (Sprite Type 6 & 7) because it was very easy to implement, requiring only setting a matching Data 1 field, sector height didn't have to be correct but it was very touch about drawing multiple sectors.
Incidentally, I got started with Build mostly by using Mapedit. Blood uses a different map format it seems, whether they are just compressed/encrypted or actually do differ I do not know.
Quick edit: Found a reference to Dark Forces when it was talking about voiceovers and a note about a moving platform "Like in ShadowWarrior" in the XSystem doc. Also this;
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Rachel
She will appear, walk towards her target location (a marker sprite), and then disappear. Any actions you wish her to perform should be accomplished with the initial trigger.
Not a difference in the engine or anything, just figured I'd stick it there as it's the first I've heard of any Rachel... Oh, lastly, there was once meant to be a weather system of sorts, some graphics exist for it in either the Alpha or the early Shareware.