I use both OOo and MS Office extensively.
OOos biggest strength is, of course, it's price. Free is always a good price, especially when you need multiple licences.
But it lags MS Office is several areas, and it's up to the user to decide whether those missing features are an issue or not.
1. Localle data. OOo gets its localle preferences exclusively from (IIRC) an ISO repository (i.e. set in stone), while MS Office gets them from the Windows localle preferences (i.e. they are user customisable). For some of my work this is inexcusable, and I CAN'T use OOo. For other work, it doesn't particularly bother me. (For those who don't follow: localle data includes your thousands separator, decimal separator, currency symbol, and so on. OOo insists on using "." as a thousands separator and "," as a decimal separator. I don't care what the ISO says they should be, my industry standards are " " and ".", and I'm not going to have my documents look like they were prepared my an illiterate two year old, because some arrogant OOo author doesn't acknowledge the existence of industry standards.)
2. Sheet length limits, this is pretty self explanatory: MS Office allows more rows and columns per sheet than OOo. If you need more than (again, IIRC) 65000 rows per sheet, you can't use OOo. Some arrogant prick from the OOo dev team commented, "If you need more than 65000 lines, you [-]should be using[/-] will use a database, not a spreadsheet.", to which I say, "**** you, if I find it more efficient to install an extra R 50 worth of RAM, than to learn an entirely new application, then that's what I'm going to do. Either cater to your customers requirements, or forever remain an also ran."
For those saying TL-DR: There is no alternative to MS Office, unless you're willing to accept OOo's faults. OOo is free and it works, but be aware of its limitations, and decide whether you can live with them, otherwise spend the grand and a half, and get a basic version of MS Office.