Why does the Torah not insert 'Chag' on Shavu'os like it does by all the other Yamim-Tovim?
Why does the Torah refer to Shavu'os as "Yom ha'Bikurim"?
Rashi: Because on Shavu'os they brought the Shtei ha'Lechem, 1 which comprised wheat from the first crops of the year.
Chizkuni: From this day and onwards one may bring Bikurim to the Mikdash.
Rashi (in Pesachim, 36b): Which permitted Korbanos from the new crops and Bikurim to be brought to the Beis-Hamikdash.
What are the connotations of "b'Shavu'oseichem"?
Seforno: It means for the sake of 1 "Shevu'os Chukos Katzir" that I guarded for you' (that the barley and wheat will ripen in time for the Omer and Shtei ha'Lechem).
Targum Yonasan: It means 'at the end of the seven-week period (of Sefiras ha'Omer).