Do the following terms have positive, neutral or negative meaning?
What are other similar terms that are used for positive, neutral and negative intention?
All the terms mentioned so far (memorable, impressive, remarkable, unforgettable, etc.) tend to have positive connotations in the absence of any negative modifier. Memorable is the most neutral of the bunch.
For equivalents to memorable that have a negative connotation, you may have to go a little further afield. Traumatic, notorious and infamous can all mean "memorable in a bad way."
Impressive has a clear positive meaning (“evoking admiration”, says the New Oxford American Dictionary). Memorable and remarkable are both supposedly neutral, and can be combined with negative events (e.g., “a memorable death”). For some reasons, I myself find remarkable as having a slightly positive tone that memorable doesn't have; others might comment in other answers or comments.
There is always unforgettable, which is neutral, and momentous, which is usually positive. Depending on the context you might also say lasting, noteworthy or historic.
Leaving a lasting mark/impression is more than a word, but also should be there
Most words here have slightly (or clearly) positive connotations. For one with a clearly negative one, try devastating.