It's very good according to The Complete University Guide. Many STEM subjects often accept entrants with higher average grades than Edinburgh according to there. Although universities with a high proportion of Scottish students (Glasgow almost certainly has a higher proportion than Edinburgh) almost certainly get overrated in entry stats if Scottish Highers for 17 year olds and some international qualifications are being regarded on a par with A-Levels for 18 year olds. Hence St Andrews, Strathclyde, and Glasgow are ranked above Cambridge for entry stats. Across all subjects, Glasgow doesn't have quite the high percentage of staff engaged in high quality research as most other top universities but the quality of that research is very good.