Lower contrast, a drop in speed, a higher level of base fog. In general unless badly stored film last well beyond the expiry date with no issues, an exception is usually the 1600/3200 emulsions.
But remember all manufacturers reduced the expiry dates on film boxes etc a few years ago, mainly when standard like ISO 9001 came in, so at one time B&W films often had an expiry date of 5 years from manufacture now it's more like 3, but if the films been factory stored it can be under 2 years by the time it reaches a dealers shelf.
Ian