As you gain levels, you can augment Create Astral Construct to increase the construct you can summon to a higher type, allowing you to pick more special abilities, and eventually abilities from a better list.
Their combat abilities seem to be increased from 3.0 for the minor constructs, and decreased for the major ones. In general the 3.0 versions were claimed to be better in combat than summoned monsters, but not as versatile since summoned monsters could cast helpful spells sometimes.
A major change in 3.5 is that you cannot summon mulitiple "lesser" constructs -- you get one construct per manifestation of the power (although you could manifest the same power in consecutive rounds to get more than one construct into the same combat).
But it is too early to tell. I have a Shaper character but haven't tested her astral constructs in combat yet. They are mainly for fighting, although if your character is small, or the construct of a high enough type, it could fly you over a pit I guess.