Goalkeeping is one of the hardest positions to judge, particularly over short periods of time.
A very good keeper will have such good positioning that they rarely need to make spectacular saves, so they might just look very average to most people. Likewise, a poor keeper might have such bad positioning, that they're constantly having to dive for everything and might look good. As well as shot stopping, there is obviously:
- Dealing with crosses (easier to judge, because it's obvious when a keeper can't do this)
- One-on-ones
- Sweeping / command of area behind the defensive line
- Communication with (and organisation of) the defenders
- General level of error-making (takes time to judge)
- Confidence to get over errors