Arkieman, these pictures aren't the greatest but they might help illustrate correct and incorrect leg structure:
Rear leg angulation from the side. 1 - correct angulation. A line can be drawn from the pin bone to through the point of the hock to the dewclaw. 2 - sickle-hocked. Legs are too far under the body and in turn place extra strain on the muscles and bones of the stifle joint, hips and legs. 3 - post legged. Legs are too far back (too little angle) and place extra strain on the stifle joint and surrounding muscles, ligaments and tendons. In a bull, post legged is a serious problem as too much pressure is placed on the joints when he mounts a female. Sickle hocked isn't quite so bad.
Front legs 1 - correct structure. The legs come out from the centre of the shoulder and straight down to the ground. Body weight is distributed evenly on the legs, feet and joints. 2 - splay footed or toed out. Knees are closer than normal and from the knee down the legs twist outward. 3 - pigeon toed or toed in. Knees are wider apart than normal and legs are bowed in appearance. Of the two faults, toed in is more serious in a bull because it tends to cause a coarse and protruding shoulder, while a slight degree of toed out is acceptable and sometimes advantageous in a bull as it tucks the shoulders in.
1 - Correct hind leg structure. Legs come out from the centre of the hindquarter and straight down to the ground. Body weight is distributed equally. 2 - cow hocked. common fault. Hocks are closer than normal and the toes turn outward. 3 - bow-legged. Hocks are wider than normal and the toes are closer.
As far as the other points: strong topline - look for a nice straight spine without dips. Shoulders should be smooth and the animal should flow nicely from the neck to shoulder to body without any jutty bits. Hips to pins - most judges will look for the hips and pins to be fairly level. I like to have the pins slightly lower than the hips to help in calving. Also width between the hips and between the pins, and length from hip to pin is indicative of pelvic capacity. Note in the diagrams above the pins, or hooks, are actually higher than the hips. This is not good - it can lead to both calving problems and more importantly urine pooling.
These diagrams and descriptions come from an excellent book called Beef Cattle: Breeding, Feeding and Showing by Lucy Newham
Also, regarding the comment about looking for too much in young calves, experience with both cattle and goats has shown me that what an animal looks like in the first few days of its life is what it will end up looking like. Arkieman was speaking about a one month old calf, so I referred to that age. But I continually assess calves, and I actually find that to my eyes, calves look best at 4 - 5 mths just before weaning, and then they begin to get a bit more gangly and out of proportion.
Arkieman, hope this all helps.