I have to agree with Designer...both look like interesting scenes that could have made for some good shots, but the composition of both is rather poor. Without having witnessed either scene in person, it's hard to make specific suggestions here...I'm sure I would have walked around a bit, look for different/better angles and perspective and such. With the waterfall shot for example, a large portion of your image is dominated by a rather featureless sky. If you were trying to do a long exposure shot of the water falls, I would have found a way to put the emphasis on that....the water falls...in other words, you try to include too much in the composition...and the same goes for the Ferris wheel. With the Ferris wheel shot you have two distinct primary elements competing with each other...the wheel and the fountain. There's probably a few ways you could have gone there...either isolate the wheel, isolate the fountain or simply move back/zoom out and make it more of a "cityscape". I think if you had of taken some time to really evaluate the elements of the scene, you likely would have walked away with a much better image. That said, being able to "see the picture" takes time. Perhaps the best advice I can offer would be to read up on the elements of composition...don't limit yourself to photography manuals (many just glaze over this concept), but look into some books on painting and even graphics design as well. Learn what actually makes a good picture good.
Beyond the composition aspect, there's a few other problems. With the Ferris wheel shot for example, I'm sure you used a moderately long exposure, however in this case it makes the Ferris wheel itself look out of focus (especially the cars). The flare on the lights suggest that you may have used a fairly small aperture (drop box wouldn't allow me to view the EXIF date online)...personally, I would have either opened up the lens and gone with a faster shutter speed (and higher ISO if needed) for a sharp image, or I might have gone to the other extreme...do a really long exposure with the Ferris wheel in motion to create a truly artistic blur (amusement park rides can be a lot of fun with long exposure after dark shots). Likewise with the falls shot, while the falls actually look pretty decent (although a bit too much silk for my own tastes), the shadows seen in the rocks are seriously underexposed. I honestly can't tell if this was simply due to how the shot was processed or if the scene simply exceeded the dynamic range of the camera (long exposure shots of water can often be tricky in that regard), but at the very least I'd try and open up those shadows (one way or another) a fair bit. Also with the falls shot, while this sort of comes back to composition, I certainly would liked to have seen a MUCH better sky in that shot...either sunshine, sunrise/sunset or drama...what you have there is really pretty blah.
Again both scenes do look quite lovely and if you have local access, both would be well worth making some future attempts....but I'd take some time, read up and do your homework first.
There is a famous quote from an expert photographer (I cannot remember his name) to the effect that if the picture does not work you are not close enough - might apply to the waterfall.
If you are wanting context for the waterfall, lowering the camera so that the river after the waterfall is well visible but less sky might help. Also, panning to the left - bringing the waterfall nearer to the centre would make the picture more harmonious.