In my opinion, love is never enough. Some people may think love consists of everything else, but I strongly disagree with that. That might be the case in a scenario where the partners would speak to each other... maybe once a year, and made eye contact once a month. Love is easily broken, and without something to fall back on, you're an easy victim for divorce.
Some other factors to consider before marriage:
1. Strong communication- The partners need to be able to converse with self-disclosure, be able to listen, and be able to give good feeback, in the majority of situations.
2. Positive conflict resolution- Every marriage experiences arguments, no matter how in love you think you are. Therefore, if you're not able to resolve these conflicts peacefully and completely, then you are bound to keep your own thoughts left on the inside because you "love" the person.
3. Good balance of individual and shared interest- No one, NO ONE, can go into a marriage expecting to be able to change someone to better adapt to him or her. These spouses are often seen as "controlling" and create and easy path to affairs or divorce.
4. Similar and realistic goals- As Ceridwen said, having similar and realistic goals, and following them through, is the key to a happy and successful marriage.
5. As michel said correctly, mutual respect. You have to be able to feel good about the person before you get married to them!
6. Financial success- There are some people who consider this a very shallow way to consider marriage. However, 57% of divorces are said to be caused by financial instability. If you have not gotten to your fullest in the career of your choice, you are doomed to stop at where you are, or even drop in your career. And therefore, many of your arguments turn to money. Not to mention the fact that you're probably gonna want to have kids. Try to support two of em on 10 bucks an hour.
7. Strong relationship prior to marriage- I would suggest five years of a relationship before marriage. That may sound like a long time, but your aim is to be married a lot longer than that. Like any piece of art, a relationship must be able to stand the test of time. And with five years+ and possible cohabitation, that is a good place to start.
8. Maturity- That was why I didn't get married until I was 30, and wouldn't reccomend most to. I would say the majority of people I know who got married before they were 25 found themselves looking around for relationships outside the marriage.
9. And of course, trust.