Heavyweight

adj. High-overhead; {baroque}; code-intensive; featureful, but costly. Esp. used of communication protocols, language designs, and any sort of implementation in which maximum generality and/or ease of implementation has been pushed at the expense of mundane considerations such as speed, memory utilization, and startup time. EMACS is a heavyweight editor; X is an *extremely* heavyweight window system. This term isn't pejorative, but one man's heavyweight is another's elephantine and a third's monstrosity.

Oppose 'lightweight'.