I didn't say better, I said "better-adapted". This is not about the species liking the new trait or not. Evolution is about evolving to be better-suited to the environment. For instance, a certain species of fish evolved legs a long time ago to adapt to marshy areas because that helped it to survive by getting away from other fish. This isn't about what we think is "good" or "bad", just what's useful.
And 100 things don't change until one finally succeeds. Something changes and then changes some more and then changes some more. Depending on the changes in the environment during that time, those changes might stop or go in reverse, too.
The above statement is not correct. Species do adapt evolutionary changes due to liking the feature. There used to be one that was pointed to all the time it slips my mind right now. Check it out you will find that this is a correct statement.
Also evolution is a process of trial and error. Yes it is true the certian features may not die out and keep evolving but most features die off only those either helpful to the species or well liked by the species survive.