The restoration of the Baphuon has take decades but the wait and many interruptions have been worth it. This is undoubtedly one of the great sites at Angkor; the most Pyramid-like of all the temples. The modern steps up to the top (almost) on the north side of the temple offer a great view. You descend by an equally steep set of steps on the south side.
But one important warning: kids under 12, pregnant women and inappropriately dressed people are not allowed in (bare shoulders seemed particularly offensive - carry a scarf in your bag and it will keep them happy). The restriction on kids does, sort of, make sense.....the climb to the top is precipitous. However, there's a question about whether - with appropriate warnings and all the doubtless legal caveats - that should be the responsibility of responsible adults. Therse is not upper age limit but I know that I'd back a 10 year old over an 80 year old to get to the top and down again.