The most disappointing aspect of the game (besides the horrendously bad ending and dialogue, of course), for me, definitely correlates with what you're saying, and that was the small amount of schematics in the game. When they were previewing this feature, it sounded as if what they were showing us was merely a small portion of what would be available in the retail product. When I started playing the game, I had no clue how many items I'd be able to create, so I literally picked up one of every miscellaneous object lying around. "I'll probably need this wooden spoon for something eventually... ohh, and this cooking pan might come in handy!" Unfortunately, I came to realize that the tiddly-winks I'd been stuffing into my inventory were mostly worthless junk, when I discovered that there were 7 schematics in the damn game.
Now, the custom items are pretty unique and I appreciated their designs, but I didn't find much use for them. Some are worthwhile, like the Dart Gun, especially for use against death claws and the Nuka Grenades are devastating against hordes of enemies. Others are just kind of worthless, like the Bottlecap Mine, which I never felt compelled to use or build (considering there's a free one at every work bench in the game). Some are just gimmicky and all around pointless, like the Railway Rifle and the Rock-It-Launcher especially.
I assumed their inspiration behind this feature was the similar system found in Arcanum: Of Steamworks & Magick Obscura. Honestly, if the people at Bethesda didn't play this game prior to making a sequel to Fallout 2, I'd be shocked, since it was developed by three of the biggest names behind the original Fallout and follows similar design principles. Coming off of this game, I had bigger expectations from Bethesda. You see, what really amplified my disappointment is that whereas Fallout 3 has less than 10 custom items, Arcanum had about 120, and pretty much every object in the game world was implemented as a component in their creation. I'll concede that there's obviously more polish and effort behind Fallout's items, but considering how few there are, it makes sense. Quality over quantity, but honestly, there's no reason their staff couldn't have given us both.