I think I would steer new learners of SE Asian scripts away from Cambodian as a first language to learn. Cambodian, while it is a beautiful script and has more-or-less regular pronunciation, also has a few odd exceptions, and complex vowel pronunciation rules. The consonants are divided into two groups, and many of the vowels are pronounced differently in the first group than in the second. That said, after learning the Thai script, Lao and Cambodian were not too hard. Either way, they are all great languages to learn.
Actually I am almost certain Thai and Lao have those consonant divisions as well, in fact I believe 3 or 4. If I am not mistaken they are still taught and are part of the tone system and/or can affect unwritten vowel selection. More certainly, the consonant classes somehow stem from the need to preserve pronunciation of Pali, a middle-Indian prakrit language (with features not present in these SEA countries' modern languages) that is used as the littoral language of Theravadin ("older school") Buddhism. See http://pali.pratyeka.org/ for more info on that.
