I need to compare if a certain date/time field is greater than/less than another date field. Can this be done in a report without calculating the same using formula/boolean fields?
Don't think so. You'll need a formula field, either direct one or something set with a workflow (or Apex code of course). If that's not feasible and conditions will change often - VF page embedded on a dashboard might be the way to go?
All our filters (in WHERE clauses, reports, listviews etc) compare field to value, not field to field. There are exceptions like lookup filters but that's not helping much.
You won't be able to pull it off with a formula built in the report itself (it'd be interesting to say
LastModifiedDate:MAX - Custom_Date_Field__c:MAX and use grouping by Id to have 1 record and thus cheat with this MAX clause). But date & datetime fields can't be used in summary formulas. More info in the summary formula help.
Salesforce is coming with this new feature soon.
Refer for more details https://success.salesforce.com/ideaview?id=08730000000BrHAAA0