It depends if or how the ticket is endorsed. If it is a full fare ticket with no endorsements then yes, you can use it on any flight (on any airline) which flies between those points; in principle this can be by any routing which is within the Maximum Permitted Mileage for tickets between those two end-points.

Cheaper fares will often be endorsed "Valid on <airline> only" in which case you can change the time and date of your reservation without reissuing the ticket, but you cannot change to another airline.

Both of these are subject to the constraints of the "not valid before" and "Not valid after" dates on the ticket.

Cheaper still are the flights which are endorsed "Valid flt/date shown". These cannot be changed, or will require a fee to be changed.

Obviously there are subtle variations on all of this with specific ticket types and specific extra endorsements, but those are the three main categories. OneWorld RTW and Circle tickets are in the second category. Any change of date/time allowed but limited to OneWorld airlines.

In all cases there is no difference in principle between e-tickets and paper tickets.