You may be looking at an 'old tool' kit of a vintage of say the 60's to 80's. The kit might have raised panel lines and be heavily riveted. The small parts may be overscale or clunky, they were designed to be produced at the limits of the injection molding process of the time.
A 'new tool' kit of the same subject as the 'old tool' kit may feature recessed panel lines and perhaps recessed rivets. The limits of the process have improved, and small parts have become better defined. Hidden details such as a full cockpit may be included where the old tool was a pilot with a peg in his side you glued to the fuselage wall. Research into the prototype may have also shown that the old kit had some shape errors which have been corrected.
New tooling is not of and by itself inherently 'better'. Some modern kit manufacturers produce kits with ridiculously small parts which drive the parts count and complexity. Why do something in 5 parts when 20 will do